Case Control Studies Flashcards
compare and contrast case control versus cohort studies
with case control studies, you are handed an outbreak and try to find the cause with questionnaires that grow more specific (outcome known before exposure) while with cohort studies you send out a questionnaire to determine the group you are going to study based on their exposure to a certain risk factor, then follow them to see the outcome
what is the worst study design to determine causality?
case reports
what are the 3 best study designs to determine causality?
random controlled trials, cohort studies, case-control studies
what can you measure with a cohort study that you usually don’t know with a case-control study?
level of exposure
what are the 2 types of cohort studies?
- prospective
- retrospective
how are retrospective cohort studies usually performed and what is an advantage of this type of study?
performed by data-mining and you can add more risk factors or layers than a prospective cohort study
define a case-control study
an analytic epidemiologic research degisn in which the study population consists of groups who either have (cases) or do not have a particular health problem or outcome (control)
how does the investigator look in a case control study?
looks back in time to measure exposure of the study subjects, then compares exposure among cases and controls to determine if the exposure could account for the health condition of the cases
give 7 characteristics of case-control studies
- observational/non-experimental
- occasionally exploratory
- explanatory (analytical)
- restrospective
- effect to cause (what made them sick?)
- both exposure and disease have already occurred
- uses comparison group (controls)
give an overview of the design of case control studies
the investigator selects cases with the disease and appropriate controls without the disease and obstains data regarding past exposure to possible etiologic factors in both groups; the investigator then compares the frequency of exposure of the two groups
what groups compose the cases in a case control study?
those who get the disease from exposed and not exposed
what groups compose the controls in a case control study?
those who do not get the disease from exposed and not exposed
what do we ask concerning odds ratios in case control studies?
we ask whether certain exposures are more common among those with disease
describe the sampling frame of a typical case control study
typically sampling only a portion of the individuals that were potentially exposed
what does relative risk help determine in a case control study?
relative risk helps to determine whether the incident of disease is associated with certain exposures
what do we rely on in case control studies to determine whether exposure to a risk factor is more common among cases versus controls and why?
we have to rely on odds ratios (chances) because likely only sampling a portion of the population that was exposed (called the reference population)
give 7 sources of controls in case control studies
- population of a defined area
- hospital patients
- probability sample of total population
- neighbors
- friends or associates of cases
- siblings, spouses, relatives
- other
what is bias?
any systematic error in study design that results in an incorrect estimation of the association between exposure and risk of disease
what is information bias?
when differences in the way exposure or outsome are measured between controls and disease groups and observers are privy to the outcome and influence data
how do you avoid information bias? (3)
- use blind studies
- struct protocols
- standardized questionnaires
describe recall bias
the individuals being questioned have different levels of recall; so cases (thanks to the trauma of illness) are likely to better recall exposures than controls
what does recall bias result in?
over or under estimation of associations between exposure and outcome
describe selection bias
poor selection of controls, in which there are differences beyond exposure
give an example of selection bias
if you are conducting a study on poverty and measles, but fail to conisder who is vaccinated against measles versus who is not
what is confounding?
when another variable (outside the one being considered) may influence the outcome of a disease
give an exmaple of confounding
if it is stated that alcoholics are more likely to develop lung cancer, so alcohol must cause lung cancer; is ignoring the fact that alcoholics are just more likely to smoke than non-alcoholics
give 2 effects of confounding
- can mislead the investigator to make associations, or miss associations, between a risk factor and a disease outcome when none or one really exists
- can cause an over or under estimation of a risk factor’s effect
give 4 advantages of case control studies
- cheap, easy, and quick
- multiple exposures can be examined
- rare diseases and diseases with long latency can be studied
- suitable when randomization is unethical (like the effects of drinking alcohol during pregnancy)
give 8 disadvantages of case control studies
- case and control selection can be troublesome
- subject to multiple biases
- direct incidencce estimation is not possible
- temporal relationship is not clear
- if incidence of exposure is high, it is difficult to show the differences between cases and controls
- not easy to estimate attributable fraction
- reverse causation is a problem in interpretation
- multiple outcomes can not be studied (cohort studies can study this though!)
