week11 - Rainfall Example The data set contains cord yield...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
STA302/1001 - week 11 1 Rainfall Example The data set contains cord yield (bushes per acre) and rainfall (inches) in six US corn-producing states (Iowa, Nebraska, Illinois, Indiana, Missouri and Ohio). Straight line model is not adequate – up to 12″ rainfall yield increases and then starts to decrease. A better model for this data is a quadratic model: Yield = β 0 + β 1 ∙rain + β 2 ∙rain 2 + ε. This is still a multiple linear regression model since it is linear in the β’s. However, we can not interpret individual coefficients, since we can’t change one variable while holding the other constant…
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
STA302/1001 - week 11 2 More on Rainfall Example Examination of residuals (from quadratic model) versus year showed that perhaps there is a pattern of an increase over time. Fit a model with year… To assess whether yield’s relationship with rainfall depends on year we include an interaction term in the model…
Background image of page 2
STA302/1001 - week 11 3 Interaction Two predictor variables are said to interact if the effect that one of them has on the response depends on the value of the other. To include interaction term in a model we simply the have to take the product of the two predictor variables and include the resulting variable in the model and an additional predictor. Interaction terms should not routinely be added to the model. Why? We should add interaction terms when the question of interest has to
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

This document was uploaded on 07/15/2011.

Page1 / 11

week11 - Rainfall Example The data set contains cord yield...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online