Data analysis. Presenting data
The set of all objects to be examined is the population, and the objects chosen from it at random form a sample; the number of objects is the sample size n. When we cannot test every object, we draw conclusions from the sample. The terms of the sample are variants; writing them in increasing order gives the variation series. If variant x₁ occurs n₁ times, x₂ occurs n₂ times and so on, the numbers n₁, n₂, … are the frequencies and W₁ = n₁/n, W₂ = n₂/n, … are the relative frequencies; the frequencies add up to n and the relative frequencies to 1. Data are shown in tables and in a frequency polygon (a broken line joining the points).
“Class sample”: each pupil writes their shoe size; the class builds the variation series and the frequency and relative frequency tables.