1. Confidence Intervals Usually set at 95 % What does that mean ?
Intervals constructed this way will contain the true mean (assuming no bias) 95 % of the time
“Interpreting a confidence interval is tricky. The confidence interval either does or does not contain the true value” What you can say is that the confidence interval, say 95% CI, is that 95% of the time, an interval calculated this way with unbiased sampling will contain the true value 95% of the time. IF you repeated your sampling 100 times and computed confidence intervals each time, 95 of them would contain the true value.