100% unnecessary

November 21, 2008

There’s a disease that has befallen the Western world. I call it percentitis. The syndrome is quite simple: Every relation, ratio, growth or decrease of some sort is quantified in percent. I think it’s unnecessary, even misleading sometimes, and just a futile attempt by the marketing drones at making boring things sound interesting. After all, “I agree 100%” is just another way of saying “I agree completely” and “I got this blender for 50% off” isn’t really that much better than “I got this blender for half the price.”

You might be right in saying that’s nitpicking. However, by far the biggest beef that I have with percent is when it’s used for quantifying an increase or decrease:

BigCorp has grown continually by 7% each year for the past four years.

Compare and constrast this with

BigCorp has grown continually by factor 1.07 each year for the past four years.

I know it sounds weird because we’re not used to saying it like that. But these incremental percentages would be just as weird to somebody who’s never heard of them. After all, they’re specifying what’s essentially a factor in (x-1)*100%. Indeed the percentage form drops an in my mind important information, the 1. I know it’s implied. I know that everybody should’ve learned this in 8th grade math. But why do we deliberately obscure the fact that it belongs there? For instance, imagine that you’d like to calculate the overall percentage by which BigCorp has grown over the total of four years. It’s ((1+p)^4 - 1)*100% where p is the percentage. Compare and contrast this with q^4 where q is the factor in the second statement. The result for this example is 1.31 or 31%, by the way, and not 4*7% = 28%, as somebody might naively think. Again, people should know the difference, but maybe they don’t. If we actually used the factor form, they might not be fooled in the first place.

Percentages might still be useful when talking about fractions, but then again, I don’t get why we don’t say 0.57 instead of 57%. It’s not really shorter or any easier to understand. I suppose it’s the same reason why we say 1000 km instead of 1 Mm (that’s a megametre): convention. So there we are. Percent: it’s absolutely useless. Don’t need it and don’t want it.

5 Responses to “100% unnecessary”

  1. But your proposed alternative scheme generates enormous amounts of redundancy! When comparing the growth ratios 1.041, 1.076, and 1.156, we keep repeating the useless “1.”, which is common to all three measures. Whereas calling them 4.1%, 7.6%, and 15.6% is more efficient because it only bothers to print the “interesting part” that we care about.

    And your proposal is even worse when applied to things that are shrinking (the current stock market, say, or the world economy). Numbers like 0.997, 0.989, and 0.891 require mental subtraction to figure out what is going on. Whereas -0.3%, -1.1%, and -11.9% show us, again, what we really care about, which is how “different from one” the fraction is.

    So I vote this proposal -100%.

  2. philikon Says:

    Brandon: Yes, the “1.” is redundant in a way, but you could argue that the “%” is redundant as well. Why say 20% growth if you could say 1.2?

    Regarding negative growth, I still think that the actual factor is more meaningful. Because a growth of -20% on year won’t be compensated by a 20% growth the next year. It will be compensated by a 25% growth. Figuring this out means having to add or subtract the invisible “1.” all the time. If I were to look at a shrinking of factor 0.8, then figuring out the compensating growth is easily obtained by taking the reciprocal value of that, 1.25.

  3. paddy3118 Says:

    You made me think of an allied pet-peeve of mine: So many graphs that miss out a natural origin.

    I constantly see graphs, especially of money related things, where the zero on one or both axis is missing. When an article is describing the change in the FTSE they may show a very limited excerpt, with the index going, say from 5000 to 5500 and so magnifying any change, which coincidentally supports their articles point of view.

    – Paddy.

  4. “Normal” people don’t properly understand decimals (as proven by the audio file at http://verizonmath.blogspot.com/2006/12/verizon-doesnt-know-dollars-from-cents.html ) and try to compensate by switching models. 😉

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