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### 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.

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.

Contingency Tables

- Two categorical variables

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)

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