Tuesday, December 16, 2008

The Magical Number Seven, Tax Collectors and Cellphone Designers

Recently I was paying some taxes. In France this is not as terrible as it sounds because the tax people have a most excellent website www.impots.gouv.fr where you can pay all your taxes online with just a few mouse clicks. The site is surprisingly effective and makes the chore of paying taxes if not exactly a pleasure then maybe less painful that it could be, though every mouse click still sucks away thousands of Euros.

But there is one area where the site might be improved, and herein lies a very general lesson not only for website design but also for the design of mobile phones and other consumer products: the way they require you to enter long numbers without spaces.

Fifty years have passed since George Miller wrote his landmark paper “The Magical Number Seven Plus or Minus Two” --
http://psychclassics.yorku.ca/Miller/ -- but the lessons have apparently not yet been learned. Following many experiments, Professor Miller discovered that the average human can process information in no more than five, six, seven, eight or at most nine “chunks” of information – seven plus or minus two. In other words if you try to remember a string of ten digits you will find that when you get to the end the first one has already fallen off the end of your working memory.
Everyone is limited to seven plus or minus two chunks, but what changes is the size of the chunk. You will be familiar with this from the days when you learnt to read. At first you mastered the individual letters, like C-A-T. After some practice you could probably recognized “cat” as a discrete chunk of information, rather than three, and by adulthood you can also handle larger chunks like “catalog”, “catalyst”, “cataclysmically” and so on”.

Many people instinctively manage large numbers in this way, breaking an indigestible long string of digits into a smaller number of bigger chunks, this making it easier to remember, read and type. Try, for example to dial the number 0033142928100 and without some help you will find it difficult to do accurately. Yet this string of 13 digits can be reorganized into larger chunks which are easier to handle, like this: 0033 1 42 92 81 00.

This is in fact the traditional French way to write phone numbers and instinctively applies the chunking technique to make numbers easier to process. In the example it is easier to digest forty-two / ninety-two, rather than four-two-nine-two. By chunking the number in this way we reduced thirteen small chunks of information to six larger chunks and the result is a significant improvement in readability, ease of memorization and ease of entry on keyboards.

You can test this for yourself by taking a list of numbers with no spaces and ask someone to type them all into the memory of a phone. Check the time and the accuracy of the entry and then compare with the result you obtain when you use the chunking technique.

The improvement is evident, yet it is not just the taxman who expects us to type in long numbers without any attempt at chunking, but also major cellphone manufacturers also sin in this respect. I have in front of me phones made by Finnish, Korean and Canadian companies – I won’t mention names to spare them embarrassment – and all three of them present memorized numbers as a long string with no spaces, making them hard to read, copy and enter.
I am sure that it would take just a minor software modification to fix this issue, and fifty two years after Professor Miller’s work it is perhaps surprising that this has not yet been done, but in a way it is encouraging for communications consultants to see that there is still a strong need for advice like this.
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