I'm Aza Raskin @aza. I make shiny things. I simplify.

I'm VP at Jawbone, focusing on health.

 

Know When to Stop Designing, Quantitatively

Interface design is more than hand waving and color preferences. When you design anything to be used by humans, there are some fundamental tools which can tell you if one interface is better than another. Quantitatively. Don’t believe me? Answer this:

Which of the following two sentences contains more information?

  1. Cogito ergo sum.
  2. Shoes smell bad.

[*] The careful reader may be waggling their finger at me. It isn’t exactly true that the first and second sentences have exactly the same amount of information. More common letters actually give less information than less common letters. Knowing that a four letter word contains an “e” and a “t” doesn’t give you much help in figuring out what the word is. But knowing that the word contains a “z” and an “m” narrows the choices down a lot. If something is more probable, it contains less information. So if you are a stickler for correctness, pretend that the second sentence was “Go rig outcomes.”

The first represents a foundational building block of Western rationalism, the second is a rather banal (albeit true) thought. The first sentence clearly has more meaning, yet they both contain the same amount of information[*]. Why’s that? Because they both have the same number of letters and use the same alphabet. To get ahead of myself slightly, they both contain they same number of bits of information.

The lesson here is that “meaning” and “information” are distinct concepts. Meaning is something which can’t be quantified, whereas information can. Meaning is subjective, information is objective. So how do you quantify information? In bits.

A bit is the fundamental unit of information. It represents the choice between two mutually exclusive things: a one or a zero; a left or a right; a Leche Flan or a chocolate mouse. (on the other hand, maybe I can have both). The choice between two things is said to contain one bit of information. Figuring out how many bits of information a choice contains is essentially a divide and conquer approach: the choice between four things can be broken into two steps of choosing between two groups of things, thus contains two bits of information. The choice between eight things can be broken into three steps of choosing between two groups of things, and so contains three bits of information. This is visually demonstrated below:

Information yielded choosing among 2 to the n objects.

As you can see, if you have some number of things to choose from–and that number happens to be a power of two–it is easy to find the number of bits of information that the choice represents: it’s just the power. What happens if your are choosing from some number of things that isn’t a power of 2? Just take the number’s base 2 logarithm. If you don’t know how to do that, don’t worry about it. Just choose the closest power of two. The most you’ll ever be off by is half a bit. Or, just enter log(number)/log(2) into Google. It’ll give you the answer.

Choosing any letter is a 5 bit choice.

Choosing any letter (e.g., “g”) is a 5 bit choice.

So back to the two sentences. There are 16 characters in each sentence, including spaces and periods. Each character represents a choice from the English alphabet plus punctuation. Let’s say that there are 32 letters and punctuation marks. That’s 25 things to choose from, so each character represents 5 bits of information. There are 16 characters, so in each sentence there is a total of 5*16 = 80 bits of information.

We’re not even touching the surface of information theory yet, and there are many cool things we could do. For instance, we could compare the number of bits per character in Japanese versus English (it turns out that English is only 60% as compact as Japanese, which explains why Japanese book are always around two-thirds the size of their English counterparts, but I’ll leave that as an exercise for the reader). For now, however, let’s side step and start applying what we’ve learned to interface design.

Efficiency

There’s one more thing to get out of the way: the definition of efficiency. Efficiency may seem like a hard thing to quantify, but engineers figured it out a long time ago. You simply divide output by the input.

For a car, the input is gas (which contains a certain amount of chemical energy) and the output is miles driven (kinetic energy). With the appropriate conversion factors, you can divide those two energies to find that your car engine has an efficiency of around 25%. That means you car’s engine is throwing away 3/4 of your gas money by heating the environment instead of making you go forward. An electric car can have efficiencies of upwards of 80%. No wonder the gas companies don’t want Detroit to go electric. But there’s an upper limit to how efficient something can be: 100%. You can’t get more energy out than you put in, otherwise you’d be able to build perpetual motion machines. And that’s something best left to crackpots and politicians.

The most important property of efficiency is that it lets you know how you are doing in the grand scope of things. If an engine has an efficiency of 10%, you know you can do a lot better. And if an engine has an efficiency of 98%, no matter how brilliantly you design, you won’t be able to improve it much.

Efficiency lets you know when you can stop looking for a better design.

The same is true in interface design, where we use a measure called information efficiency. This is simply the minimum amount of information needed for the task divided by the information actually input by the user.

Time for an example.

Digital Wrist Watches

I wrote an article called A Pretty Neat Digital Watch a little bit ago, where I talked about how confusing and inhumane setting a digital watch is. We are now equipped to calculate exactly how bad it is.

To find out how (in)efficient digital watches are to set, we need two pieces of information: how much information is minimally needed, and how much information the user inputs.

Let’s start by figuring out how much information is minimally needed. For simplicity, let’s assume we are only setting time to the minute (so no need to worry about seconds) and that we are ignoring AM/PM considerations.

There are sixty minutes in an hour and twelve hours on a clock. Thus there are 60*12, or 720 possible times to which we can set a watch. 720 is roughly 29.5. Therefore, we know that setting the time requires a minimum of 9.5 bits of information.

So far so good. All we need now is to know how much information it takes to set a digital watch.

The buttons of a digital watch.

The buttons of a digital watch.

Digital watches generally have four actions needed to set the time: press SET, press and hold SET, press MODE, and press SPLIT/RESET. That means any one of those actions represents 2 bits of information because there are 4 = 22 choices of actions.

Now, to actually set the time, one does:

  • Press and hold SET. (1 key press)
  • Press MODE to select the hours place. (1 key press)
  • Press SPLIT/RESET to advance hours. (6 key presses on average)
  • Press MODE to select the minutes place. (1 key press)
  • Press SPLIT/RESET to advance minutes. (30 key presses on average).
  • Press SET when done. (1 key press)

Counting the key presses yields an average of 40 presses to set a digital watch. Each press represents 2 bits of information, so setting a watch requires 40*2 = 80 bits of information.

Stop to reflect on what that means: setting the time on a digital watch requires the same amount of information as trying to type the sentence “cogito ergo sum”. If someone told you to type that on a watch with only four buttons, you’d tell them they were crazy. Yet you’re doing the equivalent every time you try to set a digital watch.

We can now calculate the efficiency of the setting a digital watch. Remember, the efficiency of an interface is the minimum amount of information needed over the information the user inputs. In this case, 9.5 bits/80 bits, which roughly equals .12, or 12% efficient. We are throwing away almost 90% of our effort.

If you bought a bicycle that was only 12% efficient, you’d return it immediately. With a bicylce like that you’d barely be able to ride along a flat road, let alone attempting a hill.

Analogue Wrist Watches

Digital watches have a lot of room for improvement. Common sense says they’re pretty bad and our calculated efficiency agrees. What can efficiency tell us about analogue watches?

There are two possible actions in setting an analogue watch: choosing whether the watch is in the time-setting mode, and turning the crown to actually set it. The first action represents 1 bit of information (the crown can either be pushed in or pulled out), and the second action represents 9.5 bits of information (there are 720 possible times to which the watch can be set).

Setting an analogue watch requires:

  • Pulling out the crown. (1 bit)
  • Turning the crown to the right time. (9.5 bits)
  • Pushing the crown back in. (1 bit)

In total, 11.5 bits of information is required of the user so the efficiency is 9.5 bits/11.5 bits or 82% efficient. That’s pretty good! Much better than the 12% of the digital watch.

[*] The astute reader may have a burning question at this point: “Doesn’t releasing the crown also yield 1 bit of information?”. The answer is no, but the reason is subtle.

Imagine that your parents are coming over to your place and you want to surprise them by playing their favorite soundtrack. The problem is, you don’t like it very much. You go out and buy the CD but you want to wait until just before they come to start playing it, so you have your friend stand outside and signal you when your parents arrive.

My claim is that your friend’s signal doesn’t convey any information about whether your parents are coming. Why? Because you know your parents are coming. There is no alternative. This isn’t a binary choice between 0 (your parents coming) and 1 (your parents not coming). There is only 0 (your parents coming) and the choice among one thing represents 0 bits of information (20=1).

But your friend giving you a signal clearly contains some sort of information. You know more after his signal, so what’s going on?

The signal isn’t giving you any information about whether your parents are coming, instead it’s giving you information about when your parents are coming. And that’s the subtle, but important, distinction.

If all you care about is if something is going to happen–and it is guaranteed that it will happen–then the fact of when it happens is unimportant. On the other hand, if you do care about when something happens, then even though the fact of it happening doesn’t contain information, the when of it does.

So back in our quasimodal analogue watch. We know that after setting the time the crown will automatically return to the non-pulled state, but we don’t care when it will happen. Because we don’t care about the information conveyed by when, there is no information conveyed by the crown automatically returning.

But 82% is still aways from 100%. There should be something we can do to increase the efficiency. The efficiency increase will have to come from pulling or pushing the crown to choose the time-setting mode. What happens if we used a time-setting quasimode instead of a mode? That is, what if we made the crown spring-loaded, so that we would never have to push the crown back in? It would knock-off the final 1 bit of user-input[*]. Thus the efficiency would be 10.5 bits/9.5 bits, or 90% efficient. Of course, one has to be careful to take ergonomics into account: the crown would have to return to it’s original position slowly enough that one wouldn’t have to continually pull the crown out again.

As a short aside, this is a general benefit of using quasimodes: not only does it increase efficiency by eliminating one action, it also decreases mode related errors. Also remeber that efficiency is a single measure: it does not predict how fast a interface is to use, or how easy it is to learn. When designing an interface, optimizing efficiency must be balanced against other considerations.

And now, because we are way up at 90% efficiency, we know that we can stop looking for a better solution.

But one could cheat. If the watch is atomic-clock set, as I described in A Pretty Neat Digital Watch, the user would never have to do a thing, and the efficiency would jump to the vaulted perfection of 100%.

Warning, Warning: Efficiency at 0%

On the other end of the spectrum are those monstrosities of interfaces. The places and devices that require input from the user when no input should be required. These are the times when the computer is simply wasting our time: the second most egregious crime a computer can commit. (The most egregious crime being destroying our work.)

An error message with 0% efficiency.

An error message with 0% efficiency.

For example, I still come across websites that give me alerts like this:

This has an efficiency of 0%. There is only one thing that I can do. I can either click “OK”, or wait and click “OK” (or even click the “X”, which does the same thing as clicking “OK”). I have no choice. So the action of clicking doesn’t represent any information. You’d think that such dialog boxes would only appear on web sites circa 1994, but in the latest version of Word, I found one lurking.

word_error.png

A common error message from Word with 0% efficiency.

To all designers out there: please never do this. There’s no excuse.

Interfaces with an efficiency of 0% also exist outside the world of poorly designed dialog boxes. There is one in particular that’s so ubiquitous that we use it every time we use a computer.

The Desktop!

Think about it: if you want to write a letter, how much of the letter do you get written on the Desktop? None. If you want to look something up in Wikipedia, how much of the searching do you get done on the Desktop? None. If you want to perform a calculation, how many numbers get crunched on the Desktop? None!

The time you spend fiddling with your Desktop to get where you need to go to get your work done is entirely wasted. You get no work done on the Desktop. It has an efficiency of 0%. Clearly, there is a lot of room for improvement on the Desktop.

The Shortcomings of Efficiency

Efficiency is a tool that should be included in the arsenal of every designer. It is the only tool that gives a quantitative measure that can compare any given interface to the best possible interface. It’s like magic: you can compare any interface to the best possible interface without knowing what that is!

But, efficiency is not the end-all of interface design. Efficiency doesn’t let you know how fast an interface is, or how often people will make mistakes, or how hard your interface is to learn. Efficiency doesn’t quantify beauty (although is something of a proxy to elegance). The humaneness of an interface simply cannot be reduced to a single number: sometimes highly efficient interfaces can be entirely inhumane. But even a full battery of GOMs modeling, focus groups, and user testing can only show you the mistakes of your current design.

Efficiency can tell you when you need a new inspiration.

RT @aza Know When to Stop Designing, Quantitatively | Follow @aza on Twitter | All blog posts

View all 124 comments



Anonymous

Here is the justification as to why that dialog is still in Office:
http://blogs.msdn.com/jensenh/archive/2006/06/14/629189.aspx
Though I do agree they could have come up with something better.
An interesting article.


    yorumun ilginç ama aydınlatıcı değil biraz daha yardımcı olursanız seviniriz…



stet

And the bit about watches shows why overdesigning things generally makes them worse: if the crown pops back in every time it is released (in the search for this 100% efficiency) you’ve actually made it far less efficient and massively increased the number of pull-crown-out instances.

Under the spring-load model, for every rotation of the crown, when the fingers are reset to the start position for another rotation, the crown will pop back in, and have to be pulled back out again.
Pull
Turn
Pull
Turn
Pull
Turn

instead of
pull
turn turn turn turn
push.


A fascinating article! This really excites me to learn more about information theory.

But I’m confused about your claims that the desktop is “0% Efficient.” I would agree for the examples you give, but it sounds like you’re simply picking arbitrary “would be nice” scenarios that the Desktop doesn’t attempt to satisfy.

For instance, my wristwatch is also 0% efficient, when it comes to making french fries.

Perhaps you could perform your analysis on something the desktop is much better suited to, like “make sure I save a file from an email attachment.” Often this involves a quick “click, drag, release” action, where saving to another location would require navigating through a number of intermediate steps.

I’m not sure I would be able to correctly identify the number of bits of information for something like this. How do you deal with situations like “picking a spot in a file system” where the bits of information can vary widely. Just pick an arbitrary task like “choose a folder 4 levels deep?”



LKM

[This is pretty much a copy of my post on Michael Tsai's Blog:
http://mjtsai.com/blog/2006/07/23/quantitative-design/
Sorry about that]

Isn’t the “returning crown” the same as the “OK” button in the last dialog boxes? Anyway, the information in those boxes isn’t in the button, it’s in the text. Perhaps your definition of “information” is a bit non-standard:

I think your “amount of information is equal to number of bits” explanation is wrong, even considering “probability of a letter,” if I remember information theory and Shannon correctly. Which you actually show with the “Japenese” comparision: Do japanese books contain less information because they’re shorter? Even if they’re a translation from an english book?

Second, your “Efficiency lets you know when you can stop looking for a better design” meme is wrong. It’s true if you’re designing for robots. If you’re designing for humans, it’s wrong, because humans learn, and even “worse,” they constantly forget and thus are forced to re-learn. The most efficient interface is only the most efficient interface for a user who uses the interface correctly. But the whole issue of interface design is that users *never use the interface correctly* and that we thus need to design interfaces which work for people who are “stupid” from the POV of the programmer.

Your article is interesting, but in my opinion (and it’s possible that I’m missing something) quite useless for real-world interface design unless you’re designing an interface to be used by robots, or unless you’re trying to decide between two usability-wise comparable interfaces.


A very interesting read! It captures many of my “usability intuitions” and provides a solid theoretical framework for interface thought.

To support the latter claim:

I think the Japanese/English comparison actually illustrates information theory quite nicely: If the Japanese translation of an English book preserves all information of the original (=total information is eqal) and is shorter (= contains fewer individual letters), then the individual letters have to carry more information. So LKM’s first argument seems faulty to me.

As to LKM’s second argument: Granted, the greatest challenge in interface design is the user misinterpreting interfaces and forgetting usage details. But that’s exactly the reason why the information efficiency account is so useful: A simpler interface in terms of the number of choices the user is forced to make (which is just another way of talking about the amount of information he has to deal with) reduces the probability of the user misunderstanding or forgetting something, and at the same time reduces learning time.

Of course there are other factors, such as consistency and given conventions, that contribute to the usability of an interface. But I think Aza got it right that none of them is as fundamental as information efficiency.



Marcus Sundman

Ahem… setting the digital watch:

  • Press and hold SET. (1 key press)
    Press MODE to select the hours place. (1 key press)
  • Press and hold SPLIT/RESET to advance hours. (1 key press)
  • Press MODE to select the minutes place. (1 key press)
  • Press and hold SPLIT/RESET to advance minutes. (1 key press).
  • Press SET when done. (1 key press)

So now we’re at 13.5 bits, but the last step can be automated (i.e., return to normal mode after a short timeout) so we’re really at 12.5 bits. That’s not bad, considering it has the huge additional advantage of there being no risk of the time getting wrong because of any slight movements when a crown goes back in.



Marcus Sundman

In fact, you can even “optimize” away the MODE presses, too, if you have this psychotic need to minimize data flow (as if that would somehow make it better in itself). We just add small delays, so that after SET is pressed the “focus” (e.g., blinking digit) shifts forward if you don’t do anything for a while (e.g. 2 seconds). Then we have:

  • Press and hold SET. (1 key press)
  • Press and hold SPLIT/RESET to advance hours. (1 key press)
  • Press and hold SPLIT/RESET to advance minutes. (1 key press).

That’s 10.5 bits.
Since we are at 90% efficiency now it’s apparently time to stop designing.


so isn’t there a simpler reason that the letting go of the crown doesn’t count as a bit of information? If you picked up a rag to wipe off a window, and then you dropped it again, the picking up of it had to be orchestrated, thus counts as bits in information, but gravity, just doing it’s thing, doesn’t. So if the watch acts on it’s own, to “complete” the process, it, like gravity must take the ownership of the bit — not the user.


While I agree with you on the Microsoft Word dialog, the Javascript popup was, at one time, a good design decision. Back in the day, sending information over the line was expensive, and you couldn’t use Javascript to re-write your page. The popup box was the best alternative, because it saved having to reload the entire form if you missed a necessary field.

Even though that was a long time ago, it still brings up an important point – sometimes those zero-choice efficiency boxes actually do have a choice in them. The choice the user makes is the length of time the box is in existence, and in this case they are very efficient. There is a huge difference between the box lasting 1 seconds and 10 seconds This has to happen when the information you are presenting to the user is transient, e.g. messages that obscure the application, messages that are warnings about some condition that need to be delivered to the user regardless of the application they are using (and therefore cannot write into that application).



LKM

I think the Japanese/English comparison actually illustrates information theory quite nicely: If the Japanese translation of an English book preserves all information of the original (=total information is eqal) and is shorter (= contains fewer individual letters), then the individual letters have to carry more information.

That is true, but it kind of contradicts the point made in the article, namely that number of bits equal amount of information.

If you ZIP a text file, it contains maybe 10% of the bits of the original file (depending on entropy), but it still contains the same amount of information.

Obviously, that means that one bit carries more information in a zipped file (since some of the bits in the original text file are redundant), but they’re still the same bits – a 0 and a 1.

So “# of bits == # of information” simply does not work.

A simpler interface in terms of the number of choices the user is forced to make (which is just another way of talking about the amount of information he has to deal with) reduces the probability of the user misunderstanding or forgetting something, and at the same time reduces learning time.

Not true. It’s easier to learn stuff that seems more natural or obvious. Consider this: If you have a system with (N) functions and (A) buttons, the smallest amounts of steps (X) would be achieved if (A)^(X) = (N). This is basically the binary search if you have two buttons: Each time, you click a button, you narrow down the possible functions you can reach by half.

Is this a good interface? For a computer, it’s the best. For a user, it’s pretty much the worst interface possible.

Again, we need to remember that users aren’t robots. Users look at an interface as a human, trying to relate it to something they know. You need to guide users, you need to make your interface obvious. The interface with the least amount of steps is in 99% of all cases not the most obvious interface.


LKM,

as to the “# of bits == # of information” question: You have to differentiate between bits as discrete storage units and bits as statistical units of information.

An example: A text file originally consists of, say, 1000 bits of storage (0s and 1s). In compressed form, it only consists of 100 bits of storage. Since information cannot be destroyed by lossless compression, that means that both files contain at most 100 bits of information entropy. So the amount of bits1 and of bits2 doesn’t have to be the same. I think it is clear that “bit” in the original posting means “statistical unit of information”, not “discrete storage unit”.

As to the significance of information efficiency: You are right, there’s no automatism between fewer choices and better interfaces. And of course there are other factors you have to take into account, “such as error rate, user learning time, and long-term user retention of the way to use the interface”. This is cited from Jef Raskin’s exposition of the GOMS model, and I believe Aza would take a similar stand. The usefulness of quantitative accounts isn’t that they provide some automatism for interface design, but that they can be (to cite Jef again) “a useful guide for our designs”. I still think information efficiency is a fairly good heuristic for reducing interface complexity.

Of course, there are trade-offs: You have to discern cases where learning time is small compared to usage time (e.g. daily used business software) from those where software is used only occasionally. In the former case, efficiency is much more important than in the latter, while in the latter obvious but possibly inefficient interfaces might be the better choice.



LKM

I think it is clear that “bit” in the original posting means “statistical unit of information”, not “discrete storage unit”.

That’s probably the problem then, because I didn’t read it like that. In fact, the very first example with the two sentences seems to contradict that assessment. Anyway, it doesn’t matter too much, since that wasn’t really the main point of the article.

The usefulness of quantitative accounts isn’t that they provide some automatism for interface design, but that they can be (to cite Jef again) “a useful guide for our designs”.

I agree. I simply feel that it’s dangerous to introduce automatisms in interface design which will eventually lead to bad interfaces that show good results when measured.

You have to discern cases where learning time is small compared to usage time (e.g. daily used business software) from those where software is used only occasionally. In the former case, efficiency is much more important than in the latter, while in the latter obvious but possibly inefficient interfaces might be the better choice.

Agreed, and just to add to that, all users will forget things over time, and no user wants to use an application which constantly holds his hands. The best interface always strikes the sweet spot between learnability and efficiency. For some application, that sweet spot may lean towards learnability, for others, towards efficiency. There is no case where you can simply forget about one to maximize the other.



Nigel

Hi all,
I am afraid Maths (or Math as you call it) is not my strong point so I did have some trouble understanding this article. For example I still have no idea where the number 25 comes from that is used to work out there are 5 bits of information required to store a sentence of 16 characters. If you write another one of these articles please can you show and explain your working more so that more people can understand where the numbers are coming from.

Thanks in advance.



Anonymous

Having a “monologue box” that gives you information and makes you click OK is, I think, a good thing in many contexts. Specifically, it’s good when you suspect that a program may not have done what you told it to. I don’t trust MS Word enough to take it on faith that it looked through one of my documents and found no errors. I want to see evidence that it did its job.

By contrast, there’s at least one place on a Windows machine where a critically needed OK popup is missing. I’m painfully familiar with this one. The Windows Task Manager is not very good at its (admittedly very difficult) job. Suppose I click into a website that confuses my Firefox — sites with long QT clips tend to do this, for instance — and I have to click out. Uh-oh, Firefox is not responding! Better hit Ctrl+Alt+Del. Good, okay… highlight Firefox… hit End Task… wait, nothing’s happening. I’d better click again. Hm, no, still nothing. Perhaps third time’s the charm?…

I want a popup box that says “Task Manager will attempt to end the program you selected.” That way I know the computer heard me over all the voices in its head, and I can wait patiently until either Firefox closes or I have to hold down the Power key for five seconds. Instead, I’m sending it multiple End Task commands, confusing the poor thing even further.



[ICR]

In reply to Brian, have you considered what would happen if you tried to close something that didn’t take a long time to close using that design? It would be very fustrating and a waste of time on most occasions.
Also consider that it is hard enough to free resources as it is, what if your system is crawling to a halt and you need to free resources, you now have to wait for Task Manager to load, close something, wait for the dialog to appear, click ok, then repeat several times.
The best feedback would be a message or an icon by the side of the entry that would indicate it is trying to close it. Again, a non modal unintrusive solution.



Richard Karpinski

“why Japanese book are always”

“Also remeber that efficiency”

“For example, I still come across websites that give me alerts like this:
An error message with 0% efficiency.”

Never happens to me. I don’t see alerts that look much like that.

“I found this lurking:
word_error.png”

I think something other than the second line above was supposed to appear here.

The nitpicker volunteers to pick the nits before you publish them. I seem to find a lot of them.



Tarwin

I really think that the desktop, even though it may be 0% efficient (I just use Google Desktop now to load pretty much anything), I think that it is 100% needed, at least for myself.

You see, I love to feel that I have some SPACE to work in. Like a clear desk. I can’t handle having 100 different windows all open on top of each other (yes, not a Mac user), and love to occasionally “show desktop” and then open just what I’m working with. Gives me that feeling of a clean space.

Guess the only problem then is my need to fill my deskotp with 1000s of icons .. bugger!



Oscar Sart

Hi,
first of all I really appreciate your article and philosophy, but I still have a question.

I wonder how do you think that a form should be validated (even when required fields have some kind of indication to be filled in) when computer users sometimes don’t know which mouse button they have to press or how can they, for instance, print some interesting text from a non-formatted website (because when they print they get blank sheet of paper)?

You are right when saying that the problem is not from the user when he/she doesn’t understand how the microvawe works, but it is useful to drive the user to get better results more easily, don’t you think?

Best regards.

(Sorry for my bad english)
Oscar Sart


I really hate to nitpick a nice article but the first example of information theory with the two sentences is really… wrong. You made a good point that the probability distribution of letters will result in a different amount of information, but so will the person reading it. For me, I know shoes are stinky. It’s highly probable, so for me it has very little information compared to cogito ergo sum.

And you can’t gloss over this… with interfaces the end user will make a difference. Interface actions that they are familiar with may have lower information entropy compared to unfamiliar ones despite requiring more work.

Ultimately, it doesn’t detract from the premise of the article to use information theory as a tool for comparing against a theoretical limit, but I wish the beginning was less misleading.



Mike

If you take the premis behind cogito ergo sum to be correct then that statement renders 2 pieces of information against the 1 piece of information rendered by “shoes smell bad”.



Paul

Hmm, I really need to learn to keep my mouth closed. While I maintain the two sentences contain different amounts of information, I’m wrong in my comment saying that information is dependent on the reciever. Different recievers may be able to encode information more or less efficiently, but it’s the same amount of information. My bad.



karuna

Nice one. But too long :)

Totally agree with the alert boxes that we get. Really annoying.

Transparent messages are potentially good substitute. Are there any other ideas?? brainstorm??



ojw

When you’re pressing the button 30 times to advance the time, you only have 2 choices at that point – press it again to increment the time, or press the SET button to finish.

i.e. 1 bit per button-press

Add that all up, and you get about 44 bits to set the time, instead of 80


cognito ergo sum, best quote ever.


When you say that efficiency “gives a quantitative measure that can compare any given interface to the *best* possible interface” — what is the definition of “best”?

Say you have a standard “Yes/No” dialog box. A very *efficient* way to choose an option is to move the mouse either one pixel to the left (for Yes) or one pixel to the right (for No). Whereas, in a standard GUI, I have to use many more bits of information (the pixels I travel across) to point to an answer.

I don’t think anyone would reasonably consider the first option to be the best interface. However, it is more efficient by your measure. How would measuring efficiency help us in this case?



    Aza Raskin

    The definition of best is straightforward — that you are giving the interface the absolutely minimum amount of information required to finish your task. It is best because from an information theoretic standpoint, you cannot do better.

    However, there are other metrics you need to take into account to arrive at a holistic best. In engineering, you can create a 95% efficient engine that is so large as to not be practical.

    In your example, the left/right interface is more efficient than a move-your-mouse GUI. It is also more prone to errors (which an efficiency metric does not take into account). That said, the GUI is a highly inefficient way of making a binary choice — that’s why many users use the “return” key to mean yes.


Also, I don’t think I agree with the assessment of the analog watch. There are 9.5 bits of information to be communicated, but on average there are 360 actions required, if each click of the crown is an action. That’s highly inefficient!



Wade Mealing

Beautiful writing, Being a programmer one makes all kinds of stupid mistakes and hopefully learns from them.

One thing that I’ve found as a big decision on interfaces is existing habit and knowledge. Design something that is friendly, efficient and too different and it will not be accepted, I seem to make this mistake often.

Its always nice to be able to quantify when you’re “done” designing, I’ll try using this sometime.


A few nits:

Mileage has only little to do with the efficiency of the gas motor, and almost none with kinetic energy. I guess you wanted to refer to the energy at the wheels or the shaft.

I also think that the efficiency of 100% for setting the analog time is too optimistic. Set the transmission between crown and fingers to either 0 or inifity, and you can’t set the time at all, so there needs to be something tuned there.

Another addition to the analog watch, you only presented one use case for that interface. The other would be where you get a signal that right now, it’s 12 o’clock. Bell towers or news shows deliver that signal. I guess in that case, having a modal “watch, go!” button is 100% efficient? A pseudo-modal UI would perform rather bad here, I guess. So in the case where the UI needs to deal with a variety of use cases, the efficiency depends on how you weight those use cases.

Lastly, I’d compare the desktop with a toolbox. It’s not really helping to evaluate the efficiency of a toolbox by how it’s getting screws into the wall.



Chris

While I agree with this in principle I think you’ve over simplified this a bit. For one thing the stop watch can’t be compared to bits because the stop watch has four options: up, down, forward and back. I think this would be improved by setting each digit individually, but it can’t get much better than that. The problem is that time is not conducive to binary. The only way to get your 9.5 bit watch would be to ask “Is it before or after noon? Is it before or after 6? 3? 1:30? 1:15? 1:07:30?” And so on.

My point is that things humans do aren’t binary in nature, so comparison to bit efficiency is not relevant. While the wrist watch is frustrating, an efficient system is impractical.



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Colby Russell

For users reading from a feed reader, Planet Mozilla, or any other context where your style sheet doesn’t apply, some of the content of your post appears out of place. See the image below:

Content placement in “Know When to Stop Designing”



    Aza Raskin

    That is frustrating. I wonder of inline footnotes and side bars are supposed to work in RSS…



Josip

This is a fairly interesting approach, but the explanations are oversimplified and in some cases plain wrong. In many cases where you deal with large amounts of bit-wise decisions, the efficiency will by definition (output/input) be higher than any operation that requires a small number of (actions) but the time wasted on the pre-action and post-action is ignored because of the overall volume.

Other than this, the biggest problem is that this approach implies (by formula) that maximum efficiency would be achieved by placing all the options on a single plane (page).


I absolutely agree with Mike above, there is a huge difference between the two opening sentences. Cogito Ergo Sum delivers more information than Shoes smell bad.


Nigel,

The most efficient way choose one letter is the throwing away half of the cases probable each time. For example, when you play and try to win 20 questions game, you may want to ask about some general category about answer not the specific one.

Aza assumed there is 32 characters in English. It is obvious that 32 is the same with 2^5 which is more explicitly 2*2*2*2*2. Consider choose one character from 32 characters like 20 questions game. And we assume there is only answer available “Yes” or “No”. For efficiency you will ask a question “Is the character in left half of the 32 characters?” in above picture instead of “Is the charcter a?”. Because second question is less probable.

You can consider the answer of one question as single bit(0 which implies “Yes” and 1 which implies “No”). When you repeat the process 5 times over again and again, you can pick exactly one character you find.

This result is agreed with the equation above “2^n choices = n bits”, the single character of English is 5 bit because 32 can be expressed as 2^5.

I wrote a post about the origin of calculating information by this way related to this article. (The reason we count the number of cases to calculate the content of information.) I hope this answer will be helpful to you.

http://legendre.tistory.com/entry/Information-theory


thanks for share. weldone


Pages has the same egregious modal Done Searching message. It locks up the app to tell me it can’t help any more. Le sighs, even from Apple :)

Great article! I only skimmed to be honest, but it’s on the instapaper list for after dinner reading.


I absolutely agree with Mike above, there is a huge difference between the two opening sentences. Cogito Ergo Sum delivers more information than Shoes smell bad.


And the bit about watches shows why overdesigning things generally makes them worse: if the crown pops back in every time it is released (in the search for this 100% efficiency) you’ve actually made it far less efficient and massively increased the number of pull-crown-out instances.



Sex

And the bit about watches shows why overdesigning things generally makes them worse: if the crown pops back in every time it is released (in the search for this 100% efficiency) you’ve actually made it far less efficient and massively increased the number of pull-crown-out instances.


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A very interesting read! It captures many of my “usability intuitions” and provides a solid theoretical framework for interface thought.



Dave

I once wrote a search function into an application. When something was found, it was highlighted. When nothing was found, the status bar at the bottom reported Search Complete: Not Found. I had to add the stupid one-button dialog for the not found situation because I watched over and over again as our beta testors kept waiting on the search to end after it already had. Often efficiency of the interface does not take into account that humans want positive feedback of null.

Loving the articles by the way!


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We haven’t concentrated on visual style, so forgive it.


Why use an app when you can do what bicycles usually do in Toronto, ride like you own the roads, sidewalks, and anything else that they can ride on.


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That’s the seduction of simple in action, because it isn’t simple at all. We all make numerous errors using the garage door opener — moving the door in the wrong direction first, pausing the door accidentally, or hitting the button too many times after the door doesn’t respond quickly enough. It’s actually a resoundingly bad interface masquerading behind the innocence face of a single, simple button.


We haven’t concentrated on visual style, so forgive it.


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