Case Control Design
The Case Control Study Design
The important elements of a case control study
- The outcome has already occurred
- The case is a person with the condition of interest
- The control is a person without the condition of interest
When do we do a case control study?
We do a case control study when
- We want to estimate the association of different factors with the condition of interest.
- The case control design is a retrospective study design that starts from the condition of interest and then explores to see what factors were associated with the development of that condition
Examples:
a) What are the risk factors associated with gestational diabetes ?
b) What are the risk factors associated with pre-eclampsia?
c) What are the risk factors associated with preterm labour?
STOP. TAKE A MOMENT TO CONSIDER YOUR RESEARCH QUESTION.
IS A CASE CONTROL DESIGN THE MOST APPROPRIATE DESIGN?
Is your study question focused on determining risk factors associated with a condition?
| ITEM | COMMENTS |
| Define the Case | The case is a person with the condition of interest |
| How is the case defined? | |
| Describe the method(s) of ascertainment of the case | The ascertainment of the case is masked to the exposure factors of interest. |
| Where is the case selected from? | A hospital, population, screening program etc |
| What are the inclusion criteria? | |
| What are the exclusion criteria? | |
| Define the control | The control is a person without the condition of interest |
| How is the control defined? | |
| Describe the method(s) of ascertainment of the case | |
| Where is the case selected from? | A hospital, family, neighbors, population etc |
| What are the inclusion criteria? | |
| What are the exclusion criteria? | |
| Establish that controls do not have the condition of interest | |
| Define the variables of interest | |
| How are the variables defined? | Describe all variables- exposure, disease, predictor, outcomes, potential confounders and effect modifiers. Give diagnostic criteria if applicable |
| How are the variables ascertained? | Describe how the variables are measured and ascertained |
| Who and how many people ascertain the variables? | |
| Describe comparability of assessment methods or assessors if there are more than 1 | |
| Describe standardization procedures for assessment methods | |
| Describe standardization training for assessors | |
| Are cases and controls matched? | |
| Describe the variables matched for and justify selection | |
| Describe potential sources of bias | |
| Describe how bias is minimized | |
| Describe the study size | |
| Assumptions used to estimate the sample size | |
| The sample size including specific subgroup sample size if any | |
| What is the ratio of case to control? | |
| Describe statistical analysis | |
| How are missing data dealt with | |
| Describe groupings of quantitative variables with justification | |
| Describe all statistical methods including sub group analysis and interactions, sensitivity analyses, and comparisons between the cases and controls | |
| How are confounders dealt? | |
| Mention software package used for analysis | |
| Ethics committee and IRB approval |
