![]() In this vein, you can use confidence intervals to assess the precision of the sample estimate. The margin of error indicates the amount of uncertainty that surrounds the sample estimate of the population parameter. Confidence intervals are comprised of the point estimate (the most likely value) and a margin of error around that point estimate. With this in mind, how do you interpret confidence intervals?Ĭonfidence intervals serve as good estimates of the population parameter because the procedure tends to produce intervals that contain the parameter. This will be easier to understand after we discuss the graph below. Jerzy Neyman, original developer of confidence intervals. "The parameter is an unknown constant and no probability statement concerning its value may be made." And you can't choose between these two possibilities because you don’t know the value of the population parameter. For a specific confidence interval from one study, the interval either contains the population value or it does not-there’s no room for probabilities other than 0 or 1. The confidence level represents the theoretical ability of the analysis to produce accurate intervals if you are able to assess many intervals and you know the value of the population parameter. In this case, the confidence level is not the probability that a specific confidence interval contains the population parameter. Just as there is a common misconception of how to interpret P values, there’s a common misconception of how to interpret confidence intervals. Most frequently, you’ll use confidence intervals to bound the mean or standard deviation, but you can also obtain them for regression coefficients, proportions, rates of occurrence (Poisson), and for the differences between populations. If you draw a random sample many times, a certain percentage of the confidence intervals will contain the population mean. How to Correctly Interpret Confidence Intervals and Confidence LevelsĪ confidence interval is a range of values that is likely to contain an unknown population parameter. In this post, I’ll explain both confidence intervals and confidence levels, and how they’re closely related to P values and significance levels. Previously, I used graphs to show what statistical significance really means. In this series of posts, I show how hypothesis tests and confidence intervals work by focusing on concepts and graphs rather than equations and numbers. ![]()
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