PUBH 5500/7550 Biostatistics II: Assignment 6 Repeated and Cluster Analysis: Assignment Solved

PUBH 5500/7550 Biostatistics II: Assignment 6 Repeated and Cluster Analysis: Assignment Solved

 

1. 3 points: Using the ACTG dataset, fit a Cox regression model allowing for an interaction between ZDV treatment rx and the baseline CD4 cell count cd4. To create the interaction term use the syntax: gen interaction=rx*cd4. Explain what it means that the HR for interaction is less than 1.0.  

IF the HR is equal to 1 then it indicates the equal hazard in two groups. For the hazard less than 1 it will show that survival is better in one of the groups among the understudy groups of treatment ZDV

 

2. 6 points: What are the hazard ratios for ZDV as compared to placebo for patients with 500, 109, and 50 CD4 cells, respectively? To get you started, the syntax for the first number would be: lincom rx+500*interaction, hr

 

3. 6 points: Using the SOF BMD dataset run a model to test the following hypothesis: Late menopause is a protective factor that reduces the effect of time on increasing BMI among women as they age. Show your work (relevant Stata tables) and interpret the results.

            The above model depicts that with the one-unit increase in BMI, there comes an increase in the age of women with menopause by 0.02. It has been shown from the model that there is an increasing trend in the variables.

4. 5 points: Add bootstrap to the model you ran in Q3. Paste the relevant Stata tables below. How does the bootstrap change the results? Is the bootstrap needed to answer this question?

Bootstrap is the technique of resampling the dataset with replacement and creating many simulated samples. Concerning the regression models, the results of bootstrapping helped in highlighting the amount of random variation there is in regression coefficients simply because of small changes in data values.