A psychologist examines long term retention of a learned task in a sample of n = 6 rats. At 90 days of age, rats are trained on a discrimination task. Their initial performance is recorded to serve as...

A psychologist examines long term retention of a learned task in a sample of
n
= 6 rats. At 90 days of age, rats are trained on a discrimination task. Their initial performance is recorded to serve as a baseline for subsequent comparisons. Then their performance is tested four more times at 6 months, 1 year, 1 1/2 years, and 2 years of age.  The researcher wants to see if performance changes over time.  What statistical procedure would you use to analyze this data and why?