# Is there an association?

Students need to develop their intuitions about the strength of associations between two variables.

The following three scatter plots (representing a random sample from a population) show different degrees of association for two variables. Each is accompanied by an intuitive comment on the degree of association.

Association of weight and leg length for a group of136 nine-year-olds.

There is a strong positive association between the weight and length of leg for nine-year-old children.

Association of height and leg length for a second group of 136 nine-year-olds.

There is a moderate association between the height and length of leg for nine-year-old children.

Association of height and leg length for 136 eighteen-year-olds.

There is a weak positive correlation between the height and leg length of eighteen-year-olds.

The spread of the data is seen to increase as the association becomes weaker.

Some teaching advice on strength of associations and an activity on judging associations are provided.

Year 10: Use scatter plots to investigate and comment on relationships between two numerical variables

Source