A scatter graph shows whether two measurements tend to change together. It cannot prove why.
Each point on a scatter graph shows two measurements for the same person or case. In this practice survey, they are distance from the park in metres and visits in the previous seven days. The pairs are (100, 6), (200, 5), (300, 4), (400, 5), (500, 2) and (600, 1).
Put distance on the horizontal axis and visits on the vertical axis. Plot each pair separately. Do not join the respondents in order: they are different people, not stages of a journey over time.
The points generally slope down from left to right. This is a negative correlation: greater distance tends to go with fewer visits. There is an exception. The person 400 m away reports five visits, more than the four visits reported at 300 m. A positive correlation would slope upwards; no clear correlation would show no consistent direction.
A best-fit line summarises the overall trend, with points reasonably balanced on either side. It need not pass through every point or through the origin.
The pattern does not prove that distance causes fewer visits. Transport, health, spare time, entrances and route quality may also matter. Interviews and other measurements can test these explanations. Predictions beyond the measured distances are uncertain.
Step by step
Keep pairs together
Distance and visits must belong to the same respondent.
Describe the relationship
State positive, negative or no clear correlation, its consistency and exceptions.
Test the explanation
Seek evidence about other influences before claiming a cause.
Worked example: What an interview could add
The respondent 400 m away might use a shaded direct path, while someone 300 m away faces a difficult road crossing. An interview could explore that explanation. It remains a hypothesis until the route evidence is checked.
Watch out for this
A best-fit line should join every point.
It summarises the overall relationship. Joining all points introduces a sequence that paired cases do not necessarily have.
Check your understanding
What conclusion is justified by the practice scatter graph?
- Distance is proven to be the only cause of visits.
- Greater distance generally accompanies fewer reported visits, with exceptions.
- The point at 400 m must be deleted because it differs from the trend.