Understanding Robust Standard Errors

What are robust standard errors? How do we calculate them? Why use them? Why not use them all the time if they’re so robust? Those are the kinds of questions this post intends to address. To begin, let’s start with the relatively easy part: getting robust standard errors for basic linear models in Stata and […]

Stata Basics: foreach and forvalues

There are times we need to do some repetitive tasks in the process of data preparation, analysis, or presentation. For instance, we may need to compute a set of variables in the same manner, rename or create a series of variables, or repetitively recode values of a number of variables. In this post, we show […]

Stata Basics: Reshape Data

In this post, we demonstrate how to convert datasets between wide form and long form. This is also known as “reshaping data”. Reshaping is often needed when you work with datasets that contain variables with some kinds of sequences, say, time-series data. It is fairly easy to transform data between wide and long forms in […]

Stata Basics: Combine Data (Append and Merge)

When we first start working with data, usually in a statistics class, we mostly use clean and completed datasets as examples. Later on, we realize data is not always clean or complete when doing research or data analysis for other purposes. In reality, we often need to put two or more datasets together to begin […]

Stata Basics: Subset Data

Sometimes only parts of a dataset mean something to you. In this post, we show you how to subset a dataset in Stata by variables or by observations. We use the census.dta dataset installed with Stata as the sample data. Subset by variables * Load the data sysuse census.dta * See the information of the […]

Stata Basics: Create, Recode and Label Variables

In this article we demonstrate how to create new variables, recode existing variables, and label variables and values of variables. We work with the census.dta data that is included with Stata to provide examples. generate: create variables Here we use the generate command to create a new variable representing the population younger than 18 years […]

Stata Basics: Data Import, Use and Export

In Stata, the first step of analyzing a dataset is opening the data in Stata so that it knows which file you are working with. Yes, you can simply double click on a Stata data file that ends in .dta to open it, but we prefer to write syntax so we can easily reproduce the […]

Using and Interpreting Cronbach’s Alpha

I. What is Cronbach’s alpha? Cronbach’s alpha is a measure used to assess the reliability, or internal consistency, of a set of scale or test items. In other words, the reliability of any given measurement refers to the extent to which it is a consistent measure of a concept, and Cronbach’s alpha is one way […]

Getting Started with Quantile Regression

When we think of regression, we usually think of linear regression, the tried and true method for estimating a mean of some variable conditional on the levels or values of independent variables. In other words, we’re pretty sure the mean of our variable of interest differs depending on other variables. For example, the mean weight […]

Stata Tip: Name Your Graphs

An important component of data analysis is graphing. Stata provides excellent graphics facility for quickly exploring and visualizing your data. For example, let’s load the auto data set that comes with Stata (1978 Automobile Data) and make two scatterplots and then two boxplots: sysuse auto twoway scatter price mpg twoway scatter mpg weight graph box […]