In This Chapter
How to standardize scores
Ranks in files
Rolling in the percentiles
In my left hand I hold 15 Argentine pesos. In my right, I hold 100 Chilean pesos. Which is worth more? Both currencies are called pesos, right? So shouldn't the 100 be greater than the 15? Not necessarily. "Peso" is just word magic — a coincidence of names. Each one comes out of a different country, and each country has its own economy. To compare the two amounts of money, you have to convert each currency into a standard unit. The most intuitive standard for us is our own currency. How much is each amount worth in dollars and cents? As I write this, 15 Argentine pesos are worth more than $4. One hundred Chilean pesos are worth about 15 cents.
In this chapter, I show you how to use statistics to create standard units. Standard units show you where a score stands in relation to other scores in a group, and I show you additional ways to determine a score's standing within a group.
As the previous paragraph shows, a number in isolation doesn't really tell a story. In order to fully understand what a number means, you have to consider the process that produced it. In order to compare one number to another, they both have to be on the same scale.
In some cases, like currency conversion, it's easy to figure out a standard. In others, like temperature conversion or conversion into the metric system, a formula guides you.
When it's not ...