Week 2 — Summarizing Data with Tables & Graphs

Welcome to your Week 2 Start Here page.

Why this matters

A picture of data is often the first thing anyone sees. A nurse scanning patient wait times and a small-business owner reading a bar chart of sales both need to read the picture correctly and notice when it misleads.

In plain language

A list of 344 penguins, or 12 months, or the 36 ways two dice can land is hard to take in all at once. This week you learn to turn a long list into a short table and a clear picture. You will count how often each value shows up, which gives a frequency (a count of how many individuals fall in a group). You will draw the counts as bars, slices, dots, or a histogram (a bar picture of numbers sorted into equal-width ranges). Then you will learn to describe the picture's shape out loud, and to notice when a graph has been drawn to fool you.

• Already covered: Week 1, Foundations & Types of Data, taught you to tell a population from a sample and to sort every variable by type and level of measurement.
• This week: tables and graphs for one variable, the language of shape, a first look at tables that count two categories, and the tricks that make a graph mislead.
• How they connect: the type of a variable decides its picture: labels get bars or slices, and numbers get dots, stems, or bins.
• Where we're going next: Week 3, Numerical Summaries: Center & Spread, puts numbers on the middle and the spread that you only describe in words this week.

Focus

How do you turn a long list into a table and a picture that tell the truth? This week you count, draw, and read shape.

By the end of this module, you should be able to:

• [ ] build a frequency and relative-frequency table and draw it as bars or a pie
• [ ] pick a dot plot, stem plot, or histogram for a set of numbers
• [ ] name a shape's skew by its tail and read a two-way table
• [ ] spot a truncated axis or an area distortion

To-do

Plan your week

1. Read Chapter 2 (about 35 minutes), then the lecture and slides.
2. Work the lecture tutorial (60–90 minutes) and the practice set (about 20 minutes).
3. Do the Data Lab (about 90 minutes), the discussion, and the assignment.
4. Take the quiz.

This week's checkpoint: name the skew of the twelve month lengths by its tail, and say why.

You've got this

Take it in order, and ask your instructor early if a step snags.

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