1. Measures of Central Tendency
Measures of central tendency tell us something about the “typical-ness” of a set of data.
Tell us what the typical score is in a distribution of scores.
Three measures of central tendency:
Mode
Median
Mean

2. Measures of central tendency: mode
The mode is the score that occurs most frequently in a distribution.
Sometimes more than one score occurs at frequencies distinctively higher than other scores, in which case there is(are) more than one mode:
Bi-modal distributions.
Multi-modal distributions.
Only appropriate measure of central tendency for nominal data.

3. Measures of central tendency: median
The median is the middle score in an ordered distribution of scores.
It is the score that divides a distribution in half.
It is also the score at the 50th percentile rank.
The median is the most appropriate measure of central tendency for ordinal data.

4. Measures of central tendency: median
In the distribution given to the right, find the median.
What is the percentile rank (PR) of a score of 13?
What is the score cor-responding to a percentile rank of 15?
Score Freq Cum. F %c

5. Measures of central tendency: mean
The mean is the arithmetic average value of a distribution (of scores).
I Xi represents the score for individual i (in a distribution of size n) on the variable X, then
Xi / n
gives the mean of the distribution of X.

6. Measures of central tendency: mean
For the distribution of GPAs given to the right. What is the mean GPA?
Ans.: 2.71
A distribution of GPAs
Case GPA
1 2.56
2 3.04
3 2.88
4 3.25
5 1.80