From the Guidelines
The type of study described is a case-control study, where individuals are selected based on their outcome status, which is particularly efficient for rare diseases or diseases with long lead times. This study design is chosen because it allows for the efficient gathering of information about a rare disease by comparing individuals with the condition to those without it, who would have been selected for the study if they had developed the condition of interest but do not have competing exposures or outcomes related to the condition of interest 1.
Key Characteristics of Case-Control Studies
- Individuals are selected based on their outcome status, which is the disease outcome of interest
- This design is particularly efficient for rare diseases or diseases with long lead times
- Cases (individuals with the condition) are compared to controls (individuals without the condition) who would have been selected for the study if they had developed the condition of interest
- Controls should comprise a group who do not have competing exposures or outcomes related to the condition of interest, such as incidentally injured people of similar age in a hospital-based study 1
Comparison to Other Study Designs
- Unlike cross-sectional studies, which examine the relationship between variables at a single point in time, case-control studies compare cases to controls to identify potential causes or risk factors for a disease
- Unlike cohort studies, which follow groups over time to observe outcomes, case-control studies are retrospective and start with the outcome of interest
- Case-control studies are useful for rare diseases because they allow researchers to gather information efficiently without waiting for follow-up periods, as would be required in a cohort study 1
Importance of Proper Control Selection
- Proper control selection is crucial in case-control studies to ensure that the comparison between cases and controls is valid
- Controls should be selected based on the counterfactual condition, which means they should be individuals who would have been selected for the study if they had developed the condition of interest but do not have competing exposures or outcomes related to the condition of interest 1
- Matching on key confounders, such as age or sex, can also increase comparability between cases and controls, but it should be noted that any matched features cannot be evaluated for association in primary models 1
From the Research
Study Design
The type of study where a doctor designs a form and has patients fill it out for a rare disease is a cross-sectional study.
- This study design involves measuring the outcome and exposures in the study participants at the same time 2.
- Cross-sectional studies are often used to assess the prevalence of diseases, attitudes, and knowledge among patients and health personnel 3.
- They can provide insights into the causal effects of exposure on disease incidence, but may be susceptible to reverse causality and limited to assessment of disease prevalence rather than incidence 4.
Characteristics of Cross-Sectional Studies
- Participants are selected based on inclusion and exclusion criteria, rather than outcome or exposure status 2.
- The study design is observational, and the investigator measures the outcome and exposures at the same time 5.
- Cross-sectional studies can be conducted relatively faster and are inexpensive, but may be difficult to derive causal relationships from the analysis 2.
- They can estimate the prevalence of disease and odds ratios to study the association between exposure and outcomes 2.
Advantages and Limitations
- Cross-sectional studies are useful for population-based surveys and to assess the prevalence of diseases in clinic-based samples 2.
- They can provide valuable information for designing cohort studies 2.
- However, cross-sectional studies may be subject to selection and information bias, as well as confounding, when used for analytical purposes 3.