A Gentle Introduction to Stata - Second Edition

by Alan C. Acock

Alan C. Acock’s Alan Acock’s A Gentle Introduction to Stata, Second Edition is aimed at new Stata users who want to become proficient in Stata. After reading this introductory text, new users will not only be able to use Stata well but also learn new aspects of Stata easily.

Acock assumes that the user is not familiar with any statistical software. This assumption of a blank slate is central to the structure and contents of the book. Acock starts with the basics; for example, the portion of the book that deals with data management begins with a careful and detailed example of turning survey data on paper into a Stata-ready dataset on the computer. When explaining how to go about basic exploratory statistical procedures, Acock includes notes that should help the reader develop good work habits. This mixture of explaining good Stata habits and good statistical habits continues throughout the book.

Acock is quite careful to teach the reader all aspects of using Stata. He covers data management, good work habits (including the use of basic do-files), basic exploratory statistics (including graphical displays), and analyses using the standard array of basic statistical tools (correlation, linear and logistic regression, and parametric and nonparametric tests of location and dispersion). Acock teaches Stata commands by using the menus and dialog boxes while still stressing the value of do-files. In this way, he ensures that all types of users can build good work habits. Each chapter has exercises that the motivated reader can use to reinforce the material.

The tone of the book is friendly and conversational without ever being glib or condescending. Important asides and notes about terminology are set off in boxes, which makes the text easy to read without any convoluted twists or forward-referencing. Rather than splitting topics by their Stata implementation, Acock chose to arrange the topics as they would be in a basic statistics textbook; graphics and postestimation are woven into the material in a natural fashion. Real datasets, such as the General Social Surveys from 2002 and 2006, are used throughout the book.

The focus of the book is especially helpful for those in psychology and the social sciences, because the presentation of basic statistical modeling is supplemented with discussions of effect sizes and standardized coefficients. Various selection criteria, such as semipartial correlations, are discussed for model selection.

The second edition of the book has been updated to reflect new features in Stata 10 and includes a new chapter on the use of factor analysis to develop valid, reliable scale measures.

Table of contents

List of figures

Support materials for the book

1 Getting started 1

1.1 Conventions

Introduction

1.2 The Stata screen

1.3 Using an existing dataset

1.4 An example of a short Stata session

1.5 Summary

1.6 Exercises

2 Entering data

2.1 Creating a dataset

2.2 An example questionnaire

2.3 Develop a coding system

2.4 Entering data

2.4.1 Labeling values

2.5 Saving your dataset

2.6 Checking the data

2.7 Summary

2.8 Exercises

3 Preparing data for analysis

3.1 Introduction

3.2 Plan your work

3.3 Create value labels

3.4 Reverse-code variables

3.5 Create and modify variables

3.6 Create scales

3.7 Save some of your data

3.8 Summary

3.9 Exercises

4 Working with commands, do-files, and results

4.1 Introduction

4.2 How Stata commands are constructed

4.3 Getting the command from the menu system

4.4 Saving your results

4.5 Logging your command file

4.6 Summary

4.7 Exercises

5 Descriptive statistics and graphs for a single variable

5.1 Descriptive statistics and graphs

5.2 Where is the center of a distribution?

5.3 How dispersed is the distribution?

5.4 Statistics and graphs—unordered categories

5.5 Statistics and graphs—ordered categories and variables

5.6 Statistics and graphs—quantitative variables

5.7 Summary

5.8 Exercises

6 Statistics and graphs for two categorical variables

6.1 Relationship between categorical variables

6.2 Cross-tabulation

6.3 Chi-squared

6.3.1 Degrees of freedom

6.3.2 Probability tables

6.4 Percentages and measures of association

6.5 Ordered categorical variables

6.6 Interactive tables

6.7 Tables—linking categorical and quantitative variables

6.8 Summary

6.9 Exercises

7 Tests for one or two means

7.1 Introduction to tests for one or two means

7.2 Randomization 0

7.3 Random sampling

7.4 Hypotheses

7.5 One-sample test of a proportion

7.6 Two-sample test of a proportion

7.7 One-sample test of means

7.8 Two-sample test of group means

7.8.1 Testing for unequal variances

7.9 Repeated-measures t test

7.10 Power analysis

7.11 Nonparametric alternatives

7.11.1 Mann–Whitney two-sample rank-sum test

7.11.2 Nonparametric alternative: median test

7.12 Summary

7.13 Exercises

8 Bivariate correlation and regression

8.1 Introduction to bivariate correlation and regression

8.2 Scattergrams

8.3 Plotting the regression line

8.4 Correlation

8.5 Regression

8.6 Spearman's rho: rank-order correlation for ordinal

8.7 Summary

8.8 Exercises

9 Analysis of variance (ANOVA)

9.1 The logic of one-way analysis of variance

9.2 ANOVA example

9.3 ANOVA example using survey data

9.4 A nonparametric alternative to ANOVA

9.5 Analysis of covariance

9.6 Two-way ANOVA

9.7 Repeated-measures design

9.8 Intraclass correlation—measuring agreement

9.9 Summary

9.10 Exercises

10 Multiple regression

10.1 Introduction to multiple regression

10.2 What is multiple regression?

10.3 The basic multiple regression command

10.4 Increment in R-squared: semipartial correlations

10.5 Is the dependent variable normally distributed?

10.6 Are the residuals normally distributed?

10.7 Regression diagnostic statistics

10.7.1 Outliers and influential cases

10.7.2 Influential observations: DFbeta

10.7.3 Combinations of variables may cause problems

10.8 Weighted data

10.9 Categorical predictors and hierarchical regression

10.10 Fundamentals of interaction

10.11 Summary

10.12 Exercises

11 Logistic regression

11.1 Introduction

11.2 An example

11.3 What are an odds ratio and a logit?

11.3.1 The odds ratio

11.3.2 The logit transformation

11.4 Data used in rest of chapter

11.5 Logistic regression

11.6 Hypothesis testing

11.6.1 Testing individual coefficients

11.6.2 Testing sets of coefficients

11.7 Nested logistic regressions

11.8 Summary

11.9 Exercises

12 Measurement, reliability, and validity What's next?

12.1 Overview of reliability and validity

12.2 Constructing a scale

12.2.1 Generating a mean score for each person

12.3 Reliability

12.3.1 Stability and test-retest reliability

12.3.2 Equivalence

12.3.3 Split-half and alpha reliability—internal consistency

12.3.4 Kuder–Richardson reliability for dichotomous items

12.3.5 Rater agreement—kappa (K)

12.4 Validity

12.4.1 Expert judgement

12.4.2 Criterion-related validity

12.4.3 Construct validity

12.5 Factor analysis

12.6 PCF analysis

12.6.1 Orthogonal rotation: varimax

12.6.2 Oblique rotation: promax

12.7 But we wanted one scale, not four scales

12.7.1 Scoring our variable

12.8 Summary

12.9 Exercises

13 Appendix What's next?

13.1 Introduction to the appendix

13.2 Resources

13.2.1 Web resources

13.2.2 Books on Stata

13.2.3 Short courses

13.2.4 Acquiring data

13.3 Summary

Author index

Subject index