Sample variability occurs when multiple random samples are taken from the same population. For example, if I conduct four surveys of 50 people randomly selected from a given population, the differences in outcomes may be affected by sample variability. In a fifth grade class, the teacher was interested in the average age and the sample standard deviation of the ages of her students. The following data are the ages for a SAMPLE of n = 20 fifth grade students. The ages are rounded to the nearest half year: 9; 9.5; 9.5; 10; 10; 10; 10; 10.5; 10.5; 10.5; 10.5; 11; 11; 11; 11; 11; 11; 11.5; 11.5; 11.5; = Data Freq. Deviations Deviations (Freq.)(Deviations? ) X ( x - X ) ( x - x ) (f)(x - * )2 9 9.5 N 10 10.5 AA 11 11.5 The sample variance, s', is equal to the sum of the last column=... .divided by the total number of data values minus one =... S'= The sample standard deviation s is equal to the square root of the sample variance