What type of a test will I perform in R?

Question

I have a dataset which contains data observed for patients who were hospitalized for moderate or severe infection and given one of two antibiotics. The number of days each patient was hospitalized before discharge was also noted down. The analysis is divided into 2 parts;

Part 1: I have to compute if there is a significant difference between the average days of hospitalization on the two antibiotics.

Part 2: I have to compute if there is a significant difference between average days of hospitalization on the two antibiotics, after adjusting for age and severity of infection

A sample from the dataset is given below.

> head(antibiotic)

     trt age Infection.Severity Male Days.Hospitalized

1 Old Ab 41 severe 1 22

2 Old Ab 56 moderate 0 2

3 Old Ab 56 severe 1 15

4 Old Ab 66 moderate 1 15

5 Old Ab 45 moderate 1 3

6 Old Ab 41 severe 0 19

My question is, what type of a test can I use for this analysis?

Note that the treatment and infection severity data is not numerical.

Answer 1

If you want to account for variable age and sex, then there are two possibilities:

1. If any data are censored (that is, some patients are still in the hospital) then I suggest survival analysis.

2. If not, then you want some form of regression. Since "days" is an integer, you might want to use a count regression model such as Poisson or negative binomial regression. This is especially true if most of the LOS are fairly small numbers. If LOS covers a wide range of numbers, then the "regular" OLS regression might be OK - but carefully check the assumptions. OLS regression technically requires a continuous dependent variable, but if the integers vary a lot, then this usually isn't problematic.\