There’s a common saying among pediatricians: children are not little adults. You can’t take a drug therapy that works in adults and scale it down to a kid-sized treatment. Children are actively growing. Their livers metabolize drugs differently, and they have a stage of life called puberty that many of us have long forgotten. Likewise, […]

Many variables we want to measure just can’t be directly measured with a single variable. Instead you have to combine a set of variables into a single index. But how do you determine which variables to combine and how best to combine them? Exploratory Factor Analysis.

Level is a statistical term that is confusing because it has multiple meanings in different contexts (much like alpha and beta). There are three different uses of the term Level in statistics that mean completely different things. What makes this especially confusing is that all three of them can be used in the exact same […]

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.