27
Apr

Analysis of cohort studies with Stata and R

Compared to other study designs, cohort studies are somewhat more difficult to analyze because of the presence of time-dependent variables, including calendar period, age, time since first exposure, length of exposure, and cumulative exposure. Since individuals typically pass across several categories of these variables, the primary pre-analytic step is to calculate person-time at risk of observing events of interest to the correct categories of those variables. This usually amounts to create a new dataset with many records per subject and then to proceed with statistical analysis by calculating one or more frequency and association measures, including incidence/mortality rates, rate ratios (RR) with Poisson regression models, standardized mortality ratios (SMR), or hazard ratios (HR) with Cox regression models. In calculating cumulative exposure (lagged or unlagged, or within a specified time-window) an added complication is the necessity to link individual data with external exposure data (exposure matrices).

The purposes of the course are to give:

1) a theoretical overview of the analysis of cohort data;

2) practical information on how to do it with available software.

Learning objectives are:

1) to deal with time-dependent variables, with a focus on exposure matrices and cumulative exposure;

2) to work with time and dates in a statistical software;

3) to calculate person-time at risk in a correct manner, while avoiding mistakes such as immune/immortal person-time;

4) to illustrate specific commands for person-time calculation and cohort analysis available in statistical software like Stata and R.

Time Title lecturer
9:00-9:30

 

Person-years and time-dependent variables in cohort studies. Beware to mistakes: immune/immortal person-time

 

DC
9:30-10:00 Stata: how to deal with time and dates; commands for survival analysis and person-year calculation

 

MC
10:00-10:30

 

R: how to deal with time and dates; commands for survival analysis and person-year calculation

 

MS
10:45-11:00 Exposure matrices and cumulative exposure (unlagged, lagged, time-windows): concepts

 

DC
11:00-11:30 Stata: how to calculate cumulative exposure (unlagged, lagged, time-windows)

 

MC
11:30-12:00 R: How to calculate cumulative exposure (unlagged, lagged, time-windows)

 

MS
12:00-12.15

 

Stata: Rates, Poisson Rate Ratios (RR), Standardized Mortality/Morbidity Ratio (SMR), Hazard Ratios (HR): synoptic description of commands

 

MC
12:15-12.30 R: Rates, Poisson Rate Ratios (RR), Standardized Mortality/Morbidity Ratio (SMR), Hazard Ratios (HR): synoptic description of commands

 

MS