![]() had a "HR" (see below) with a mean of 0.92,.What is it saying? Looking at the "Male" line we see: Here is Confidence Interval used in actual research on extra exercise for older people: This is the risk in sampling, we might have a "bad" sample. So how do we know if our sample is one of the "lucky" 95% or the unlucky 5%? Unless we get to measure the whole population like above we simply don't know. That can happen about 5% of the time for a 95% confidence interval. ![]() Maybe we had this sample, with a mean of 83.5: Now the true mean might not be inside the confidence interval, but in 95% of the cases it will be!ĩ5% of all "95% Confidence Intervals" will include the true mean. but the true mean is inside our confidence interval of 86 ± 1.79 (in other words 84.21 to 87.79) Let's lay all the apples on the ground from smallest to largest: Now imagine we get to pick ALL the apples straight away, and get them ALL measured by the packing machine (this is a luxury not normally found in statistics!) So the true mean (of all the hundreds of apples) is likely to be between 84.21 and 87.79 True Mean ![]() Z is the Z-value = 1.960 (from the table above for 95%).There are hundreds of apples on the trees, so you randomly choose just 46 apples and get:
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