Central tendency: a statistical measure to determine a single score that defines the center of a
distribution. The goal of central tendency is to find the single score that is most typical or most
representative of the entire group.
Mean: the sum of the scores divided by the number of scores.
Population mean = μ = N
Sample mean = M = n
Weighted mean: the mean obtained when two samples are combined. Steps:
1. Determine the sum of all the scores in both samples. This sum is obtained by adding the
sum of the scores for the first sample ( ) and the sum of the scores for the second sample.
2. Determine the combined number of scores in both samples. This value is obtained by
adding the number in the first sample (n) and the number in the second sample (n).
3. Divide the sum of all the scores (step 1) by the total number of scores (step 2). Expressed
as an equation:
combined ∑ ¿ ∑ X1+∑X 2
Weighted mean = combined n = n1+n 2
Median: if the scores in a distribution are listed in order from smallest to largest, the median is
the midpoint of the list.
When n is odd: the median is the middle number.
middle pairof scores
When n is even: median = 2
Mode: the score or category that has the greatest frequency. The mode is used for nominal
Bimodal: a distribution with two modes.
Multimodal: a distribution with more than two modes.
Major mode: when two modes have unequal frequencies, this mode has the taller peak. Minor mode: when two modes have unequal frequencies, this mode has the shorter peak.
Line graph: used whe