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Exercise

Toxicology data

A toxicologist wonders if exposure to a chemical increases mortality as its dose increases. She has exposed test organisms to different doses of a chemical and recorded the number that died in each test tank. Each dose was repeated on three different days.

First, build a GLM. Building a simple model makes debugging easier. Also, you will later compare the results to GLMER. This model includes dose and replicate as a fixed-effects.

Second, build a GLMER. This time, dose is a fixed-effect and replicate is a random-effects intercept.

Last, examine the coefficient estimates with coef() from each model. Notice how the intercept estimates are displayed differently from each model.

Instructions 1/3

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  • Create glm_out, a glm() model that predicts mortality as a function of dose and replicate. Estimate an intercept for the replicate group using replicate - 1.
  • Look at the model's coefficient estimates with coef().