Distributions

Explain what a frequency distribution is

Frequencies relating to continuous data can be plotted as bars on a histogram or as a

continuous curved line on a frequency distribution.

Explain Normal Distribution

Appears as a bell-shape curve with the

following features:

• The mean, median and mode are at the midpoint of the

graph.

• The graph is symmetrical around the midpoint.

• The dispersion of data either side of the midpoint is

consistent.

For any normal distribution, 68.26% of the data will lie within

one standard deviation from the mean. 95.44% of the data lie

within two standard deviations from the mean. 99.74% of the

data are three standard deviations from the mean.

Explain what a skewed distribution is

If the data are not an even distribution either side of the mean, the

distribution will be skewed.

Explain Positively Skewed Distribution

A Positively Skewed Distribution: has most data falling below the

mean, which means the data is concentrated on the left of the

graph, with a long tail of scores to the right. It therefore contains

more low scores than high. When mode<median<mean the data

has a positive skew.

Explain Negatively Skewed Distribution

A Negatively Skewed Distribution: has most data falling above the

mean, the bulk of the scores are concentrated on the right of the

graph, with a long tail of scores on the left. It therefore contains

more high scores than low. When mean<median<mode the data

has a negative skew