Lecture 2 slides

Statistics 224

Descriptive Statistics: Numerical variables, distributions, and histograms Alyssa Digilio

Questions about course logistics 

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Have you tried to buy the Freedman et al text from “A room of one's own”? Or online?

Have you visited the course website? http://www.stat.wisc.edu/~boehm/teaching/2014/stat224/syllabus.html

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Homework 1 is posted – http://www.stat.wisc.edu/~boehm/teaching/2014/stat224/hw1.pdf

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Be sure to put your name and DISCUSSION (day and time) on the BACK of your homework

Overview of Lecture • Trends in data • Categorizing data • Categorical, continuous, or discrete

• Organizing data • Histograms

• Making mathematically valid predictions about data

World record times for the mile run

World record times for the mile run

Categorical, Continuous, and Discrete Variables • Categorical Variables • “Categories” • Ex: Do you eat breakfast?

• Continuous Variables • A variable that can take on any value • Ex: time

• Discrete Variable • A variable that is numerical, but only can take certain values • Ex: How many times have you eaten today?

Categorical, continuous, and discrete variables 

Are the following take categorical, continuous, or discrete values? - Sex - Age - Number of siblings - Height - Income - Spouse height

Histograms •A graph used to organize data •Contains bins along the X axis (typically intervals) •Contains either a count or a frequency along the Y axis •Used to show a distribution •Shows important features such as skewness, mean, and range of data

How much soda do people drink (per day)?  

Is a single number the best response? Why? With a partner, sketch (on graph paper) a distribution of (non-diet) soda consumption by persons in the USA

Daily soda consumption

Daily soda consumption

Handedness Scores 

Answer questions (Left or Right) on your index card: 1.

Writing

2.

Drawing

3.

Throwing

4.

Scissors

5.

Toothbrush

6.

Knife (without fork)

7.

Spoon

8.

Broom (upper hand)

9.

Match striking (which hand holds match)

10.

Match striking (which hand holds lid)

RIGHT – LEFT = ? RIGHT + LEFT = ? (RIGHT – LEFT) / (RIGHT + LEFT) = ?

Handedness Scores 

With a partner, draw (on graph paper) a guess of the histogram of handedness scores

Handedness Scores: Sample guess

Handedness Scores (Real data)

Who opposed the Vietnam War?

Who opposed the Vietnam War?

Review of Lecture • Trends in data can continue for short periods of time, but may not hold over long periods

• Differences between types of variables • How to read and construct a histogram • How to use mathematical reasoning to make educated guesses

References Teaching Statistics: A bag of tricks. Gelman & Nolan, 2002.