It is the set of numbers that has been observed, and from which we will make an inference to the population from which the sample was drawn. Descriptive Statistics is that branch of statistics concerned with making summary statements about sets of numbers all of which are available for inspection. Inference is the method of reasoning used to make statements about facts that have not been observed from facts that have been observed. A mean is a number which summarizes the average size of a set of numbers 10. A standard deviation is a measure of the variability of a set of numbers 11.
Variance is a measure of the variability of a set of numbers.
It is the square of the standard deviation. A Confidence Interval is a range of values within which a population parameter is estimated to lie, based on observations of sample values 14. A Confidence Interval for a MEAN is a range of values within which a population mean is estimated to lie based on observations of sample values 15. We could, of course, have either a population correlation or a sample correlation. An Interval is a range of scores between two defined values.