How large should my control group be?
Rule #1: Your control group shouldn’t be too big. Or too small. First, your control group should be about 10% of the total group of eligible customers.
Do control and treatment groups have to be the same size?
The best scenario, statistically-speaking, is an even split between treatment and control. You should not allocate less than 20% of the sample to the control condition, save for situations when you are looking for large effects (e.g., 8 point lifts) and/or using large samples (e.g., 15,000 participants).
How many people are in a control group?
The size of the control group, or any test group for that matter, depends on the size of the total population. If the experiment is run on a population size of only 100 participants, a 5% control group would be only 5 individuals, which would certainly diminish the significance of the results.
Why is a control group important in testing?
The size of the control group, or any test group for that matter, depends on the size of the total population. If the experiment is run on a population size of only 100 participants, a 5% control group would be only 5 individuals, which would certainly diminish the significance of the results.
How big should the sample size be for a control group?
You should not allocate less than 20% of the sample to the control condition, save for situations when you are looking for large effects (e.g., 8 point lifts) and/or using large samples (e.g., 15,000 participants).
Why is the size of a test group important?
As we discussed, the size of your test groups will indicate the statistical significance and the margin of error, or room for misleading results, you can expect in your outcomes. An important factor when measuring the effectiveness of a control group is the uniformity of samples.
When to reduce the size of the control group?
Minimal losses in power occur when we shrink the control size to 40% [of the sample]. A 25% to 30% range is a good compromise, as this exposes 70% of the sample to the treatment, yet still does not harm power terribly.