Module 11 Flashcards
Matching
The process of selecting the controls so they are similar to the cases in certain characteristics, such as age, race, sec, occupation, etc.
Matching can be group matching or individual matching.
Group Matching
When controls in the case-control study are selected in a manner such that the proportion of controls with certain characteristics is identical to the proportion of cases with the same characteristic
It generally requires that all of the cases be selected first
Individual Matching
For each case selected for the study, a control is selected who is similar to the case in terms of the specific variable or variables of concern
Individual matching is often used in case-control studies that use hospital controls
Source Population
The underlying cohort of people that give rise to cases
There is the potential for selection bias in case-control studies if the controls are not samples from the sour population of the cases
Advantages of a case-control study
Relatively inexpensive
Relatively short
Good for rare outcomes or those with long latency because we can recruit into the study
Can assess multiple exposures
Disadvantages
We cannot determine the temporal order
Cannot assess risk (only odds)
We are assessing prevalent cases (could be associated with survival rather than developing)
Nor good for rare exposures
Vulnerable to information bias of the exposure (differential misclassification of the exposure)
Selection bias is a major concern - should come from the same source population
Nested Control Study
the controls are a sample of individuals who are at risk for the outcome at
the time each case of the outcome develops
Case-cohort Study
the controls are randomly
chosen from the defined cohort study with which the study began. Case-control designs are advantageous because the controls are sampled from the same source population as the cases, since they all came from the same cohort study.
What distinguishes a case-control study from a cohort study
In a case control, the study begins with diseased and non-diseased people (cases); in a cohort, the study begins with exposed and unexposed people
What is the biggest source of potential bias in a case-control study
The selection of the control group
What is the main source of information bias in case control studies?
recall bias
Practical problems with matching
if an attempt is made to match to too many characteristics, it may prove difficult or impossible to identify appropriate controls - overmatching also leads to an inability to statistically analyze variables used in matching
Conceptual problems with matching
Once we have matched controls to cases according to a given characteristic, we cannot study that characteristic
The ensure the same prevalence for controls and cases
Overmatching
unplanned matching on a variable that is strongly related to the exposure being investigated in the study
multiple controls of the same type
Are used to increase the statistical power of the study
multiple controls of different types
Used to address potential control bias
What is a Nested Case Control Styd
Controls as a sample of individuals who are at risk of the disease at the time each case of the disease develops. Individually matched
Case-cohort study
Like the nested in how cases are selected, but the controls are randomly chosen from a defined cohort within which the study began. The advantage is that it is possible to study different diseases (different cases( in the same case-cohort design
What are the advantages of conducting a case-control study within a cohort study?
The problem of recall bias is eliminated,
the temporal ordering between exposure and outcome can be determined,
they are more economical (e.g., biological
samples can be analyzed for 1,000 vs. 10,000 participants), and
cases and controls are derived from the same cohort (i.e., source population), reducing the risk of selection bias.
