In other words, each Training group is represented at every Time point. The two factors of interest–Training group and Time–are crossed, as there are 9 observations from each training group in each time. The subjects in every group–endurance, strength, and concurrent training regimens–were measured on a number of physical health measures at two time points: pre and post. In this study, 27 men in their early 20s were randomized into one of three physical training groups. When you’re not sure whether two factors in your design are crossed or nested, the easiest way to tell is to run a cross tabulation of those factors. If they are nested, you cannot because you do not have every combination of one factor along with every combination of the other. If two factors are crossed, you can calculate an interaction. All combinations of categories are not represented.
In other words, an observation has to be within one category of Factor 2 in order to have a specific category of Factor 1. In other words, there is at least one observation in every combination of categories for the two factors.Ī factor is nested within another factor when each category of the first factor co-occurs with only one category of the other. Two factors are crossed when every category of one factor co-occurs in the design with every category of the other factor. It’s an important design feature that affects the analyses you can and should conduct. But once you have at least two factors, you need to understand whether they are nested or crossed. When there is only one factor in a design, you don’t have to worry about crossing and nesting. Whether the factor is observational or manipulated won’t affect the analysis, but it will affect the conclusions you draw from the results. Observational categorical predictors, such as gender, time point, poverty status, etc., are also factors. Experimental manipulations (like Treatment vs. In experiments, or any randomized designs, these factors are often manipulated. One of those tricky, but necessary, concepts in statistics is the difference between crossed and nested factors.Īs a reminder, a factor is any categorical independent variable.
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