An average tells you the center of your data. A confidence interval (CI) tells you how precisely you've estimated that center.
Use just the average when:
- You only need to describe the observed data.
- You're reporting a straightforward summary, such as “the average test score was 82.”
- You're not trying to generalize from your sample to a larger population.
Use a confidence interval when:
- You have a sample and want to say something about the broader population.
- You want to communicate uncertainty or precision around your estimate.
- You're comparing groups or treatments and want to know whether differences are compatible with random sampling variation.
- The reader needs more information than a single point estimate provides.
For example, suppose you measure the average blood pressure of 100 people:
Average = 128 mmHg
That doesn't tell us how precisely 128 estimates the population average. If you report:
Average = 128 mmHg (95% CI: 125–131)
you're saying that the data are consistent with a population average somewhere around 125–131 mmHg, under the assumptions of the confidence-interval procedure.
A useful rule of thumb is:
Average = “What did we estimate?”
Confidence interval = “How uncertain is that estimate?”
So, in research or inferential statistics, it's often better to report both, rather than choosing one or the other.