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Data with two variables

Displaying data with two variables

When investigating the relationship between two quantitative variables we draw a scatterplot.

  • When drawing a scatterplot the convention for plotting graphs applies.
  • The independent variable is placed on the horizontal axis.
  • The dependent variable is placed on the vertical axis.
  • When looking at the graph, you need to consider the:
    • Form — does it resemble a straight line or another type of function?
    • Direction — if it is resembles a straight line, what direction is it going (positive — up, or negative — down)
    • Scatter — are the points scattered close to a line or do they have a large scatter?
  • If the relationship appears to be a straight line you can draw a line of best fit.