= Solution
Measurements from the same person share baseline strength and likely share an individual response to training. An <ordinary linear model> with independent errors treats all 600 readings as independent conditional on week; that fails to represent their within-person <correlation>. The <regression residuals> can remain associated even when the population mean is linear in time. A <random intercept> captures differences in baseline strength, and a <random slope> can additionally describe differences in progress.
Back to article page
