CHAPTER 1STATISTICS

Statistics is a way of reasoning, along with a collection of tools and

methods, designed to help us understand the world

READ THE BOOK

Think Show Tell For Example Step-by-Step What can go wrong* What have we learned?

CHAPTER 2DATA

Information together with its context Numerical Names Labels

Five W’s Who, What, When, Where, Why How

WHO Respondents: Individuals who

answer a survey Subjects or Participants: People on

whom we experiment. (Experimental Units)

Records or Cases: Rows in a database or data table. Individuals about whom or about which, we have the data.

WHAT

Variables Characteristics recorded about each

individual. These are usually columns in a data table, and they should have a name that identifies what has been measured.

Categorical (or Qualitative) Quantitative (Numerical values with

measurement units) Ordinal

…more W’s

Where and When? Country? Year?

How? How the data was collected?

Why? Reason for the study

Exercise

Investments. According to an article in Fortune (Dec.28, 1992), 401(K) plans permit employees to shift part of their before-tax salaries into investments such as mutual funds. Employers typically match 50% of the employees’ contribution up to about 6% of salary. One company, concerned with what it believed was a low employee participation rate in its 401(k) plan, sampled 30 other companies with similar plans and asked for their 401(k) participation rates.

Identify the W’s

Who ? 30 Companies

What ? Participation Rates

Quantitative (Units : Percent)

When ? Sometime after 1992

Identify the W’s (cont.) Where ?

USA Why ?

The company was concerned with its participation rate compared with other companies

How ? Companies were sampled using an

unspecified method

Exercise Flowers. In a study appearing in the

journal Science a research team reports that plants in southern England are flowering earlier in the spring. Records of the first flowering dates for 385 species over a period of 47 years indicate that flowering has advanced an average of 15 days per decade, an indication of climate warming according to the authors.

Identify the W’s

Who ? 385 species of flowers over 47 years

What ? First flowering date

Quantitative (Units : days)

When ? Not specified

Identify the W’s (cont.)

Where ? Southern England

Why ? Researchers associate this behavior

with climate warming How ?

Observation. ( Method not specified)

Chapter 3. Displaying and Describing Categorical Data Make a picture First Make piles

Organize the counts by categories in a frequency table (counts) or a relative frequency table (percentages)

Both types of tables describe the distribution of the categorical variable because they name the possible categories and tell how frequently each occurs

The Area Principle

The area occupied by a part of the graph. It should correspond to the magnitude of the value it represents

Bar Charts A bar chart displays the distribution of

a categorical variable, showing the counts for each category next to each other for easy comparison.

Bar Chart

0

200

400

600

800

1000

First Second Third Crew

Class

Fre

qu

en

cy

Pie Charts Relative proportion

(percentages instead of counts).

Pie charts show the whole group of cases as a circle, each of the pieces has a size proportional to the fraction of the whole in each category.

Pie Chart

15%

13%

32%

40% First

Second

Third

Crew

Contingency Tables Two categorical variables

First Second Third Crew Total

Alive 202 118 178 212 710

Dead 123 167 528 673 1491

Total 325 285 706 885 2201Su

rviv

al

Class

Marginal and Conditional distributions Marginal Distribution

Distribution of either variable alone (at the margin of the table)

Conditional Distribution A distribution in one variable for only those

individuals satisfying some condition on another variable.

Note : If the distribution of one variable is the same for all categories of another we say that the variables are independent.

Exercises

Step-by-Step page 31

What can go wrong Check the charts on pages 34

Simpson’s Paradox (page 35)