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2 min read•october 28, 2020

Peter Cao

5-7% of the test

Roughly 2 to 3 multiple choice questions

After covering single-variable statistics, it’s time to increase the complexity a little bit with two variable statistics! We can deal with two variable statistics in two ways. With categorical variables, we can use two way tables to represent the relationship between two different categories of categorical variables. With quantitative variables, we can show the relationship between these using scatterplots. We will also see whether there is a relationship between two variables in both situations. This will link to later units as well. Our study of two-way tables will link to probability (Unit 4) and Chi-squared tests for homogeneity or independence (Unit 8). Our study of scatterplots will link to regression inference as well (Unit 9).

Three of the College Board's mathematical practices for AP Statistics are used in this unit, which will be outlined below.

**Selecting Statistical Methods**

This is useful when we decide whether we want to use two-variable statistics methods and the type to use or to use inference techniques learned later on.

**Data Analysis**

Using data analysis, we’ll figure out how to figure out different statistics from two-variable data sets and also find ways to model with them and draw conclusions.

**Statistical Argumentation**

In this unit, we will learn to argue about the strength of how much variables are related to each other, and also the most important sentence of this unit: **correlation does not imply causation!**

Categorical Variables

Two Way Tables

Joint Relative Frequencies

Marginal Relative Frequencies

Conditional Relative Frequencies

Side-by-side bar graphs

Segmented bar graphs

Mosaic plots

Correlation

Quantitative Variables

Scatterplots

Form

Direction

Strength

Unusual features (gaps, clusters, outliers)

Correlation Coefficient

Linear Regression (Least Squares Regression)

Extrapolation

Residuals

r, R^2. and s

Influential Points

Transforming Data Sets

Browse Study Guides By Unit

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Blogs

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Free Response Questions (FRQs)

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Multiple Choice Questions (MCQs)

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Unit 1: Exploring One-Variable Data

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Unit 2: Exploring Two-Variable Data

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Unit 3: Collecting Data

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Unit 4: Probability, Random Variables, and Probability Distributions

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Unit 5: Sampling Distributions

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Unit 6: Inference for Categorical Data: Proportions

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Unit 7: Inference for Qualitative Data: Means

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Unit 8: Inference for Categorical Data: Chi-Square

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Unit 9: Inference for Quantitative Data: Slopes

Practice your typing skills while reading Unit 2 Overview: Exploring Two-Variable Data

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