Statistics for CSAI 2

by Albert Major

Multiple Regression with Polynomials

1. Course context

• You are in the last month of the course.
• Three more lectures introduce new material: polynomial regression, mixed models, growth curves.
• These topics are the most complex parts of the course.
• Lecturer encourages attending lectures and practicals.
• The concepts build on everything learned so far.
• Final November meeting will be an exam Q&A and wrap up.

2.1 Intercept in dummy coding

• Question: what does the intercept represent in multiple regression with dummy coding for three groups
• Correct answer: the mean of the reference group.
• Reminders:
  • Reference group’s mean is the intercept.
  • The regression coefficients for the dummy variables show the change in mean relative to that reference group.
  • Grand mean only appears under unweighted effects coding, not dummy coding.

2.2 Polynomial order

• Question: predicted quadratic relationship between X and Y, which polynomial order
• Correct answer: 2
  • Second order gives a quadratic curve.
  • Fourth order would be quartic.
• Students rated their comfort level. Lecturer reminded:
  • If you feel lost, rewatch lectures, review examples, ask questions.

1. Introduction to polynomial regression