Standard content

Real survey data is never tidy. In this project you clean a class survey, compare two groups with the mean and the median, and write a short honest report. It uses only what you learned in the first three chapters. The code boxes only need Run and a few changed numbers.

What's inside

1. Plan the survey and clean the data: Real data has mistakes: a typing error, a value that cannot be true, a blank. Decide what values are sensible, find the ones outside, check them with the source, fix them in a copy and keep the original. One bad value can move the mean a long way, while the median hardly moves.
2. Compare groups and write the report: To compare two groups, find the mean and the median of each, and say how many were asked, because small groups can mislead. To combine two group means, add the totals and divide by all the students, never average the two means. A good report has the question, the method, the numbers, a graph and one honest limit.
3. Coding the survey: one table, many groups: A real survey is one table with a row for each student and a column for each answer. A short program can split the rows into groups by a label, such as the way to school, and give each group its count, mean and median. It can also check every value against a sensible range in one pass. Small groups swing: one unusual student moves a small group's mean much more than a large group's.