Question

A cell phone company collected data of texting speed in words per minute according to time in minutes. Explain why a scatterplot is used to represent the data, including the purpose of scatterplots.

Answer 1

A scatterplot is appropriate because you have two quantitative variables for each observation — time (minutes) and texting speed (words per minute) — and you want to show how they relate. In a scatterplot each observation is plotted as a point with its time on the horizontal axis and its speed on the vertical axis, so you can immediately see the joint behavior of the two variables.

Purpose and what a scatterplot reveals:
- Direction of association: Do points trend upward (speed increases with time), downward (speed decreases), or show no clear trend?
- Form: Is the relationship roughly linear, curved, or more complicated?
- Strength: Are the points tightly clustered around a pattern (strong association) or widely spread (weak association)?
- Outliers and clusters: Points that do not follow the pattern or groups of similar observations stand out.
- Basis for prediction: You can fit a trend line (e.g., a regression line) to make predictions of speed from time.
- Visual check before further analysis: It helps decide appropriate models and whether assumptions (linearity, homoscedasticity) might hold.

Note: a scatterplot shows association, not causation. If the data are measured repeatedly in time and you want to emphasize the sequence, you can add lines connecting points, but the scatterplot itself is the standard first step for examining the relationship between two numeric variables.