Central Tendency and Variability

Statistical Methods in Psychology

What are measures of central tendency?

Descriptive values that represent the center or middle of a data distribution (mean, median, mode).

Mean

The average, found by adding the entire set of scores then dividing the sum by the number of scores.

Median

The middle number in a distribution, found by ordering the data by lowest to highest.

Mode

The value that occurs the most in a dataset.

Variability

How spread out a group of scores is (low variability = scores cluster close together, high variability = scores are far apart).

Measures of Variability

How spread out data values are (range, standard deviation, variance).

Range

Distance from the lowest score to the highest score, found by subtracting the lowest value from the highest value.

Standard Deviation

The average distance that score fall from the mean, found by taking the square root of the variance.

Variance

The average squared deviation.