Title: What are confidence intervals? | Simply Psychology
Headings: What are Confidence Intervals in Statistics?
What are Confidence Intervals in Statistics?
What does a 95% confidence interval mean?
Why do researchers use confidence intervals?
How do I calculate a confidence interval?
Confidence Interval Formula
An Example
How can we be confident the population mean is similar to the sample mean?
How to report a confident interval APA style
How to reference this article:

Content: Therefore, as the sample size increases, the range of interval values will narrow, meaning that you know that mean with much more accuracy compared with a smaller sample. We can visualize this using a normal distribution (see the below graph). For example, the probability of the population mean value being between -1.96 and +1.96 standard deviations (z-scores) from the sample mean is 95%. Accordingly, there is a 5% chance that the population mean lies outside of the upper and lower confidence interval (as illustrated by the 2.5% of outliers on either side of the 1.96 z-scores). Why do researchers use confidence intervals? It is more or less impossible to study every single person in a population so researchers select a sample or sub-group of the population. This means that the researcher can only estimate the parameters (i.e. characteristics) of a population, the estimated range being calculated from a given set of sample data. Therefore, a confidence interval is simply a way to measure how well your sample represents the population you are studying. The probability that the confidence interval includes the true mean value within a population is called the confidence level of the CI. You can calculate a CI for any confidence level you like, but the most commonly used value is 95%.