Contents	Introduction	Descriptive	Hypothesis	Tables	Appendix

Mode: The most frequently occurring score. A distribution of scores can be unimodal (one score occurred most frequently), bimodal (two scores tied for most frequently occurring), or multimodal. In the table below the mode is 32. If there were also two scores with the value of 60, we would have a bimodal distribution (32 and 60).

Median:The point on a rank ordered list of scores below which 50% of the scores fall. It is especially useful as a measure of central tendency when there are very extreme scores in the distribution, such as would be the case if we had someone in the age distribution provided below who was 120. If the number of scores is odd, the median is the score located in the position represented by (n+1)/2. In the table below the median is located in the 4^th position (7+1)/2 and would be reported as a median of 42. If the number of scores are even, the median is the average of the two middle scores. As an example, if we dropped the last score (65) in the above table, the median would be represented by the average of the 3^rd (6/2) and 4^th score, or 37 (32+42)/2. Always remember to order the scores from low to high before determining the median.
 

Variableè	Age	ç Also known as X
	24
	32	ç Mode
	32
	42	ç Median
	55
	60
	65
n=	7	ç Number of scores (or cases)
	310	ç Sum of scores (Xi=each score)
	44.29	ç Mean

Mean: The sum of the scores ( ) is divided by the number of scores (n) to compute an arithmetic average of the scores in the distribution. The mean is the most often used measure of central tendency. It has two properties: 1) the sum of the deviations of the individual scores (Xi) from the mean is zero, 2) the sum of squared deviations from the mean is smaller than what can be obtained from any other value created to represent the central tendency of the distribution. In the above table the mean age is 44.29 (310/7).

Weighted Mean: When two or more means are combined to develop an aggregate mean, the influence of each mean must be weighted by the number of cases in its subgroup.

Wrong Method:
 

Correct Method: