division of scores into tenths or ten equal units. For example, the sixth decile is the point at which 60 percent of the scores fall below, whereas the ninth decile is the point at which 90 percent of the scores fall below

a score indicating the percentage of people or scores that occur at or below a given score. If you have a rank of 75, this means that you did as well or better than 75 percent of the students in the class

Indicates how many standard deviations a score is above or below the mean. A Z score is s standard score distribution with a mean of zero and a standard deviation of 1

A method of assessing the degress to which a specific condition is inherited; a comparison of the prevalance of a characteristic in fraternal versus identical twins