5.4 Describing Continuous Variables Across Groups

Sometimes we want to describe a continuous variable separately for different groups. For example, we might want to know the average test score for each condition, the average scale score by class level, or the average response time by group.

In jamovi, this is often done using Split by.

When to Use Split By

Use Split by when you have:

  • a continuous variable you want to describe
  • a categorical variable that defines groups

The continuous variable goes in the Variables box. The categorical grouping variable goes in the Split by box.

For example:

Continuous variable Split by variable
Exam score Study condition
Depression total score Clinical group
Boredom mean score Class level
Mind wandering score Gender

Why Split-By Descriptives Matter

Split-by descriptives are often the first step before group comparisons. Before running an independent t-test or ANOVA, you should understand what the group descriptives look like.

However, descriptive differences are not the same as inferential evidence. If one group has a higher mean than another group, that tells us what happened in the sample. It does not, by itself, tell us whether the difference is statistically meaningful or likely to generalize beyond the sample.

WarningDescriptive Differences Are Not the Same as Inferential Evidence

When you split a continuous variable by a categorical variable, you may see that one group has a higher mean than another group. That is useful information, but it does not tell you whether the difference is statistically meaningful or likely to generalize beyond your sample.

For now, describe what you see. Later, inferential tests such as t-tests and ANOVA will help us decide whether group differences are large enough, relative to variability and sample size, to reject a null hypothesis.

Running Split-By Descriptives in jamovi

To describe a continuous variable across groups:

  1. Go to Analyses.
  2. Select Exploration.
  3. Select Descriptives.
  4. Move the continuous variable into the Variables box.
  5. Move the categorical grouping variable into the Split by box.
  6. Select the statistics you want for each group.

Useful statistics often include:

  • N
  • Missing
  • Mean
  • Median
  • Std. deviation
  • Minimum
  • Maximum

Interpreting Split-By Descriptives

When interpreting split-by descriptives, ask:

  • How many observations are in each group?
  • Are any groups very small?
  • Which group has the highest mean or median?
  • How variable is each group?
  • Are the minimum and maximum values plausible?
  • Do the descriptive patterns suggest a question for inferential testing later?
WarningCommon Mistake

Do not write that one group is “significantly higher” than another group based only on descriptive statistics. Statistical significance requires an inferential test.

TipCheck Your Understanding

You want to describe average boredom scores separately for each class level. Which variable goes in the Variables box and which goes in the Split by box?

Answer

The boredom score goes in the Variables box because it is the continuous variable being described. Class level goes in the Split by box because it defines the groups.