The act of assigning numbers or symbols to characterisics of things according to a set of rules z-scores. Show were scores fall relaive to the average. A set of numbers whose properies model the properies of the objects to which the numbers are assigned. Nominal scales: numbers are used to classify and idenify, numbers are subsituted for names/labels, actual numbers chosen are arbitrary, ex. males = 1, females =2. Interval scales: contain equal intervals between numbers, therefore, it is meaningful to calculate averages, zero point has no intrinsic meaning (ex. zero degrees celsius does not mean absence of temperature) Raio scales: contain equal intervals between numbers, has a true zero point (ex. zero height has no height, can form raios (ex. 2 meters is twice as tall as 1 meter) Measures of central tendency: where a distribuion is centered. The sum of all scores, divided by the number of scores.