You are investigating whether psychotic behaviour has a physiological basis. Specifically, you suspect that the substantia nigra, a small dense mass of the brain, is reduced in psychotic individuals....

You are investigating whether psychotic behaviour has a physiological basis. Specifically, you suspect that the substantia nigra, a small dense mass of the brain, is reduced in psychotic individuals. It is known that the average diameter for the substantia nigra in human adults is 13 millimetres. You obtain the brains of 15 deceased psychotic adults and dissect them to measure the substantiae nigrae. Your measurements are as follows (measure-ments in millimetres):

Diameter 11, 15, 7, 14, 9, 12, 16, 9, 8, 11, 13, 12, 15, 12, 11

Determine from these data whether the substantiae nigrae of your psychotic sample are indeed reduced.