The Numbers Game Chapter 1: "Counting: Use Strawberry Jam"
In this chapter, the authors make a very simple point. Whenever you see a number being reported, it means that
something, somewhere, has been counted in some way. The number was not just handed down from on high -- there was some
activity involved in coming up with the number. In particular, someone had to come up with a definition of
what was being counted, and with a method of
how the counting would be done. And there can be a great deal of complexity, messiness, and arbitrariness that is hidden in those details of "what" and "how".
While this seems blindingly obvious, it is often forgotten, because we associate numbers with perfectly regular patterns that allow no room for confusion or ambiguity, such as the actual abstract activity of counting that we learn in kindergarten: one, two, three, four, and on it goes in perfect order. Lulled by this illusion of perfect regularity and orderliness, it can be easy to forget that the real world usually doesn't work like that. Rather than be mesmerized by a reported number as if it was God-given, it is important to try to understand the "what" and the "how" of the counting activity that has been performed, in all its often opaque complexity. The authors suggest thinking of
"strawberry jam" as shorthand for what counting in real life resembles: something soft, mushy and amorphous, rather than something hard as a diamond.
To illustrate this point, the authors consider a number of examples, all of them quite relevant to the kinds of numbers we see reported today:
1. US Centenarians: how many centenarians (people 100 or older) are there in the US?
Well, how would you find out? One way would be to ask people how old they are and take down their answers. This is what the US Census Bureau does. Using this method, the answer came back that there were about 106,000 centenarians in the US in 1970.
Job done? Hardly. The
actual number of centenarians in the US at the time is believed to be closer to 5,000, or about
one-twentieth of the self-reported number. Basically, many very old people have no idea of how old they are. Others know but are forgetful. Still many others lie for this or that reason. The Census Bureau tries to come up with a "preferred estimate" like 5,000 by doing extensive cross-checking with the Social Security Administration, Medicare and other agencies. Still, 5,000 is no better than an educated guess.
2. "Yob Britain": a survey that made a lot of noise in the UK in 2005 suggested that "1 in 4 teen boys claims they have done a robbery, burglary, assault or sold drugs". The press had a field day with this, with headlines screaming that the UK was raising a whole generation of "yobs" (thugs or bullies).
The thing to do is look at the definition.
What was actually counted? While the quote above mentions "robbery, burglary or assault", the vast majority of the self-reported "crimes" were instances of
assault. Next, how was "assault" defined in the survey? Here is what the survey question actually asked:
Quote:Have you ever used force or violence on someone on purpose, for example by scratching, hitting, kicking, or throwing things, which you think injured them in some way?
Please include your family and people you know, as well as strangers.
58% of assaults turned out to be instances of "pushing or grabbing". And 36% were against siblings. So as the authors say, "anyone who pushed a brother or sister six times leaving them no worse for the wear is counted as a 'prolific offender'". Anyone who pushed a little brother or sister even once and left a bruise would be counted as a "serious offender" since the offense led to injury, and be bracketed together with drug dealers, burglars, juvenile murderers and so on.
In other words, the definition used in this survey (the "what") was so
ludicrously broad that the "1 in 4" number
loses all meaning. In fact, what is more stunning about this number is that 3 of 4 teen boys self-reported as being lifelong little angels who never pushed or shoved a friend or a sibling. And that brings us to the "how" of this number -- self-reported answers to a survey, which have
no necessary relation to reality.
3. Bullying in US schools: this example is similar to the previous one. A US study reported the alarming finding that 30% of children in the US in grades 6-10 had "moderate to frequent involvement in bullying". This seems like a huge number but again we need to look at the definition.
First, "involvement" encompassed both the supposed perpetrators
and victims, both the putative bullies and those being "bullied". Second, "moderate bullying" was defined as happening "sometimes". Finally, and most importantly, here is how "bullying" was actually defined in the survey:
Quote:Bullying can take three forms: physical (hitting, kicking, spitting, pushing, taking personal belongings); verbal (taunting, malicious teasing, name calling, making threats); and psychological (spreading rumors, manipulating social relationships, or engaging in social exclusion, extortion, or intimidation).
As Joel Best, who studied this example in his book "More Damned Lies and Statistics", remarked: "does anyone remember high school"? Again, with this kind of fantastically broad definition, the real thing to marvel at is that the figure arrived at the survey is 30%, rather than closer to 100%.
There are more examples in the chapter but these suffice to illustrate the point being made here. Don't imagine a number, just because it is a number, as possessing some sort of special hardness and brilliance. Think strawberry jam, not diamonds. Think of how the number was arrived at --
what was being counted (the definition),
how was this done (the method). Many claims that appear to be implausible or sensational on their face dissolve under closer inspection because the actual definition of what was being counted does not match the common sense expectation of what the correct definition would be; or because the method used to arrive at the number was flawed or error-prone; or some combination of both.
The lesson of this chapter is:
Be alert to the "what" and the "how" of counting; remember that it is usually a complex human activity; don't imagine that real-life numbers have a special hardness or brilliance; don't think diamonds, think strawberry jam.