Title: Significance and Confidence Intervals | SkillsYouNeed
Headings: Statistical Analysis:
Significance and Confidence Intervals

Statistical Analysis:
Significance and Confidence Intervals
Statistical Significance
Null and Alternative Hypothesis
Calculating Significance
An example will make this clearer.
Confidence Intervals
Calculating the Confidence Interval
It is easiest to understand with an example.
Standard deviation for confidence intervals
Understanding z score or z value
Assessing Your Confidence Interval
Conclusion

Content: Finding a significant result is NOT evidence of causation, but it does tell you that there might be an issue that you want to examine. There is more about testing for significance of sample means, and testing differences between groups, in our page on Hypothesis Development and Testing. Confidence Intervals
A confidence interval (or confidence level) is a range of values that have a given probability that the true value lies within it. Effectively, it measures how confident you are that the mean of your sample (the sample mean) is the same as the mean of the total population from which your sample was taken (the population mean). For example, if your mean is 12.4, and your 95% confidence interval is 10.3–15.6, this means that you are 95% certain that the true value of your population mean lies between 10.3 and 15.6. In other words, it may not be 12.4, but you are reasonably sure that it is not very different. The diagram below shows this in practice for a variable that follows a normal distribution (for more about this, see our page on Statistical Distributions ). The precise meaning of a confidence interval is that if you were to do your experiment many, many times, 95% of the intervals that you constructed from these experiments would contain the true value. In other words, in 5% of your experiments, your interval would NOT contain the true value. You can see from the diagram that there is a 5% chance that the confidence interval does not include the population mean (the two ‘tails’ of 2.5% on either side).