This article is part of the Stata for Students series. If you are new to Stata we strongly recommend reading all the articles in the Stata Basics section.
This page contains links to articles describing the statistical topics covered in Sociology 357 at UW-Madison. The articles assume you're already familiar with the basics of Stata, especially Managing Stata Files and Doing Your Work Using Do Files.
SSCC staff try to keep this list up-to-date, but your instructor may add to or take away from it at any time and information you receive from him or her about what material you are responsible for always takes priority.
Frequencies for a Single Categorical Variable
For a variable that describes categories (like sex or race) rather than quantities (like income) frequencies tell you how many observations are in each category. These are examples of univariate statistics, or statistics that describe a single variable.
Categorical variables are also sometimes called factor variables. Indicator variables (also called binary or dummy variables) are just categorical variables with two categories. Frequency tables for a single variable are sometimes called one-way tables.
Summary Statistics for a Single Quantitative Variable
For a variable that describes quantities (like income) the mean tells you what the expected value of the variable is, and the standard deviation tells you how much it varies. However, the median and percentiles often give you a better sense of how the variable is distributed, especially for variables that are not symmetric (like income, which often has a few very high values). These are also univariate statistics.
Quantitative variables are often called continuous variables. Means are often called averages, and variance is just the standard deviation squared. The median is also the 50th percentile.
Frequencies for Two Categorical Variables
For two categorical variables, frequencies tell you how many observations fall in each combination of the two categorical variables (like black women or hispanic men) and can give you a sense of the relationship between the two variables. These are examples of bivariate statistics, or statistics that describe the joint distribution of the two variables.
Tables of frequencies for two variables are often called two-way tables, contingency tables, or crosstabs.
Summary Statistics for One Quantitative Variable over One Categorical Variable
For a quantitative variable and a categorical variable, the mean value of the quantitative variable for those observations that fall in each category of the categorical variable can give you a sense of how the two variables are related. Of then the question of interest is whether the distribution of the quantitative variable is different for different categories. These are also examples of bivariate statistics.
Frequencies for Three or More Categorical Variables
For three or more categorical variables, frequencies will tell you how many observations fall in each combination of the variables and give you a sense of their relationships just like they did with two categorical variables. These are examples of multivariate statistics.
Summary Statistics for One Quantitative Variable over Two or More Categorical Variables
For a quantitative variable and two or more categorical variables, the the mean value of the quantitative variable for those observations in each combination of the categorical variables can give you a sense of how the variables are related just like they did with a quantitative variable and one categorical variable. These are examples of multivariate statistics.
Last Revised: 7/18/2016