CAS Exam MAS-II Spring 2019, Question 2
Study guide: Exam MAS-II
In the supplemental material, you have been given a case study, "Systolic Blood Pressure Case Study", showing the results of different treatment options and the description of how that study was set up. You have also been asked to evaluate three statements regarding the results of the study.
The relevant output from the case study is reproduced below.
Distribution of the response (change in systolic over one year, 2,099 patients):
## change_systolic
## Min. :-8.3653
## 1st Qu.:-2.6882
## Median :-1.1343
## Mean :-0.7265
## 3rd Qu.: 0.9967
## Max. : 9.0491
Box plot of change in systolic by patient age
Model 1 — main effects of treatment and age, hospital as a random effect, constant variance, fitted by REML:
## AIC BIC logLik
## 7327.429 7361.313 -3657.715
Model 5 — the same model but with variance a function of patient age, fitted by REML:
## AIC BIC logLik
## 7328.156 7367.687 -3657.078
##
## Combination of variance functions:
## Structure: Exponential of variance covariate
## Formula: ~Age/2
## Parameter estimates:
## expon
## 0.00581435
I. Using a linear mixed effects model is not appropriate, since the dependent variable is not normally distributed. II. The age effect should have been modeled with a quadratic term. III. One should assume that variance in the change in systolic pressure is a function of the age of the patient rather than assuming constant variance.
Determine which of the above statements are true.
- A) I only
- B) II only
- C) III only
- D) I, II and III
- E) The answer is not given by (A), (B), (C), or (D)
Answer this question and see the worked solution