Once you’ve imported your data into Stata the next step is usually examining it. Before you work on building a model or running any tests, you need to understand your data. Ask yourself these questions: Is every variable marked as the appropriate type? Are missing observations coded consistently and marked as missing? Do I want […]

SPSS has a nice little feature for adding and averaging variables with missing data that many people don’t know about. It allows you to add or average variables that have some missing data, while specifying how many are allowed to be missing.

In our previous posts, we’ve relied on Stata’s pre-loaded datasets to perform analyses. But when you’re working with your own data, you’ll need to know how to import it into Stata. To demonstrate how this process works, we will use the Iris dataset from UCI. Download the dataset, then move it to whichever directory you […]

Binary logistic regression is one of the most useful regression models. It allows you to predict, classify, or understand explanatory relationships between a set of predictors and a binary outcome.

You might be surprised to hear that not only can linear regression fit lines between a response variable Y and one or more predictor variables, X, it can fit curves too. There are many ways to do this, but the simplest is by adding a polynomial term. So what is a polynomial term and how […]

Have you ever wondered whether you should report separate means for different groups or a pooled mean from the entire sample? This is a common scenario that comes up, for instance in deciding whether to separate by sex, region, observed treatment, et cetera.

Item Response Theory (IRT) refers to a family of statistical models for evaluating the design and scoring of psychometric tests, assessments and surveys. It is used on assessments in psychology, psychometrics, education, health studies, marketing, economics and social sciences — assessments that involve categorical items (e.g., Likert items).

How do you know when to use a time series and when to use a linear mixed model for longitudinal data? What’s the difference between repeated measures data and longitudinal?

No matter what statistical model you’re running, you need to go through the same steps.  The order and the specifics of how you do each step will differ depending on the data and the type of model you use. These steps are in 4 phases.  Most people think of only the third as modeling.  But […]

If you’ve tried coding in Stata, you may have found it strange. The syntax rules are straightforward, but different from what I’d expect. I had experience coding in Java and R before I ever used Stata. Because of this, I expected commands to be followed by parentheses, and for this to make it easy to […]