Scatter Plot Math Example 4

Follow the full solution, then compare it with the other examples linked below.

Example 4

hard
A scatter plot of age (x)(x) vs. reaction time (y)(y) shows a curved upward pattern (reaction time increases with age, faster for older individuals). Why would fitting a straight line to this data be problematic?

Solution

  1. 1
    The relationship is non-linear (curved), so a straight line would systematically underestimate reaction time for young and old individuals and overestimate for middle-aged
  2. 2
    Residuals would show a clear pattern (not random), violating the linearity condition for regression
  3. 3
    A linear model would have poor fit (low r2r^2) and misleading predictions outside observed range

Answer

A straight line is inappropriate for curved data; it produces systematic errors in prediction and violates regression assumptions.
The form of a scatter plot determines which model is appropriate. A curved pattern requires non-linear models (quadratic, exponential, etc.). Forcing a linear fit creates biased predictions and untrustworthy inference.

About Scatter Plot

A scatter plot is a graph with one quantitative variable on each axis where each data point is plotted as a dot, revealing relationships between the two variables.

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