What is Bivariate Data?
Data that involves two variables measured on the same subject or object. We collect pairs of values to see if a relationship exists between them.
In everyday life, we often wonder whether two things are connected — does more studying lead to higher grades? Does taller height mean longer arm span? When we measure two things at once for each person or object, we get bivariate data.
Each data point is an ordered pair , where is called the independent variable (the one we choose or control) and is called the dependent variable (the one we measure or observe).
Example pairs of variables:
- Hours of study and test score
- Temperature and ice cream sales
- Height and shoe size
In each case, we suspect that knowing one value might help us predict the other.
Think of bivariate data like a two-column table in a spreadsheet — one column for each variable, and every row is one observation. The two columns belong together, like two sides of the same story.
Scatter Graphs (Scatter Diagrams)
A type of graph that displays bivariate data by plotting each data pair as a point on a coordinate plane. It helps us see whether a relationship exists between two variables.
To draw a scatter graph:
- Place the independent variable on the horizontal axis.
- Place the dependent variable on the vertical axis.
- Plot each data pair as a single point — do not join the points with a line.
- Label both axes with the variable name and units.
Example: Plot the following data on a scatter graph.
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | |
|---|---|---|---|---|---|---|---|
| 5 | 8 | 10 | 13 | 16 | 18 | 20 |
Plot the points , , , , , , on a grid with on the horizontal axis and on the vertical axis.
Notice how the points seem to follow an upward trend — as increases, also increases.
Always give your scatter graph a title and label both axes with variable names and units. In MYP assessments, missing labels cost marks!
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