Lesson 22 of 1524
Sampling and data
A parameter describes the population. A statistic describes the sample.
Practice this chapterThe population is the whole group you care about. The sample is the part you actually observe. You rarely know a parameter. You compute a statistic and use it to infer.
Qualitative data are labels. Quantitative data are numbers, and those numbers are discrete when you count them and continuous when you measure them. How you sample — simple random, stratified, cluster, systematic, or convenience — decides whether the statistic can stand in for the population.
The four words
population → parameter sample → statistic
The Greek letter usually names the population. The Roman letter names the sample.
Worked example
A college has 12,000 students. You survey 80 of them and find that 60% work. Which numbers are the population, the sample, and the statistic?
- 1The population is the whole group the question is about: all 12,000 students.
- 2The sample is the part you actually observed: the 80 students who answered.
- 360% was calculated from those 80 answers, so it describes the sample. A number computed from a sample is a statistic.
- 4The matching parameter would be the percent of all 12,000 who work. The survey did not measure that number.
Result: Population 12,000, sample 80, statistic 60%
Why. 12,000 names who you want to know about, 80 names who you asked, and 60% is a calculation from the people you asked. That last number is a statistic because it comes from the sample, not from the whole college.
Convenience sampling asks whoever is easy to reach. That statistic describes the people who were easy, not the population.
Practice margin
This chapter
A fresh set from this chapter only. Choose 10 or 20. Multiple choice and fill-in, with no repeat inside the set.