Stage 3

What is a Randomized Complete Block Design?

July 24th, 2023 by

Designing experiments would always be simple if we could just randomly assign subjects to different treatment conditions with no other restrictions. Unfortunately, that doesn’t always work.

For example, there are many experimental situations where the subjects aren’t independent of each other. The subjects that are related to each other are combined into clusters called “blocks.” It can happen due to practicalities of running an experiment efficiently or you can intentionally plan it as a way to reduce random variance.

In either case, this is a randomized complete block design. It’s a great design to become familiar with because it will greatly expand your ability to create and analyze experiments.

How It Works

When you have subjects that share characteristics with one another, it can sometimes be difficult to isolate those characteristics directly. This makes it hard to record them as additional variables. By identifying the subjects that are similar, you can still capture how those characteristics affect the outcome. Subjects that are similar are grouped into “blocks.”

From there, you can make treatment assignments so that you put subjects from the same block into different treatment groups.

Why different treatment groups? Suppose subjects from the same block were assigned to the same treatment group. (more…)

Member Training: Linear Model Assumption Violations: What’s Next?

June 30th, 2023 by

What do you do if the assumptions of linear models are violated?

Member Training: Interactions in Poisson and Logistic Regression

May 1st, 2023 by

Interactions in statistical models are never especially easy to interpret. Throw in non-normal outcome variables and non-linear prediction functions and they become even more difficult to understand. (more…)

The Difference Between the Bernoulli and Binomial Distributions

February 8th, 2023 by

You might already be familiar with the binomial distribution. It describes the scenario where the result of an observation is binary—it can be one of two outcomes. You might label the outcomes as “success” and “failure” (or not!). (more…)

Member Training: Translating Between Multilevel and Mixed Models

October 31st, 2022 by

Multilevel and Mixed models are essentially the same analysis. But they use different vocabulary, different notation, and approach the analysis considerations in different ways.

Member Training: Analyzing Likert Scale Data

August 31st, 2022 by

Is it really ok to treat Likert items as continuous? And can you just decide to combine Likert items to make a scale? Likert-type data is extremely common—and so are questions like these about how to analyze it appropriately. (more…)