Name That Study Design
Obtaining histories and other important information from a group of known cases and from a comparison group to determine the relative frequency of the exposure under study
Case Control
Key Elements of Design: prospective, use of control groups, use of placebo, randomization, levels and purpose of blinding, Phase 0-IV trials
Sources of Bias: related to selection of participants, exposure and outcome ascertainment, non-compliance, withdrawals or losses from study
Randomized Controlled Clinical Trials
The relation between exposure and disease is different for those who participate or are selected and those who would be theoretically eligible for study, including those who do not participate.
Selection Bias
risk/rate in the treatment group relative to the risk/rate in the control group
[A / ( A + B )]/ [C ( / C + D )]
Relative Risk/ Rate Ratio
the study of how disease is distributed in populations and the factors that influence or determine this distribution.”
Epidemiology
Study of the long-term risk of cancer in men who have recently quit smoking
Cohort (Prospective)
Key Elements of Design: can be prospective, retrospective, or hybrid; use of blinding possible; selection based on exposure
Sources of Bias: related to assessment of outcome; quality and quantity of data; losses due to non-response, death or attrition/lost to follow-up; healthy worker effect
Cohort (Considered the “gold-standard” of observational studies.)
A flaw in measuring exposure or outcome that results in differential quality or accuracy of information between compared groups;
Information Bias (also called misclassification or observational bias.)
percent reduction in the incidence rate attributable to the intervention; i.e. percentage of outcome that could be prevented by using the intervention rather than the standard approach
Efficacy
a simple model of disease causation that suggests that disease is a product of the interaction between the human (or animal) host, an infectious or other type of agent, and the environment which promotes exposure.
The epidemiologic triad
12 women with uterine cancer and 12 without were contacted and asked about use of estrogen. Women were matched on age, race, and parity.
Case-Control Study
Key Elements of Design: retrospective, selection based on disease, population-based vs. hospital-based control selection, purpose of matching
Sources of Bias: related to poor ability to recall past exposures, detection bias, selective survival, Berkson’s bias, errors in data recording or transcription, inability of participant to understand question or articulate answer
Case- Control
the association of a third factor with both the exposure and the outcome
Confounding
The incidence of a disease that is attributable to exposure in the exposed group
Amount by which the risk of disease is increased/decreased for the exposed (due solely to the exposure) compared to the unexposed
a/(a+b) - c/(c+d)
Attributable Risk
excess occurrence (more than expected) of a disease or infectious agent in a specified population or geographic area; number of cases indicating the presence of an epidemic depends on the agent, size and type of exposed population, previous experience with the disease, and time/place of occurrence
Epidemic
Physical exam records of incoming freshman class of 1935 were examined in 1977 to see if weight and height at admission were related to development of CHD by 1986.
Retrospective Cohort Study
Key Elements: snapshot of health experience of the population, simultaneous exposure/disease classification, population sampling design, public health planning and disease burden/prevalence
Sources of Bias: self-selection, non-response, selective survival, inability to understand or articulate, poor ability to recall, probing/leading questions
Cross-sectional
The association between exposure and outcome depends on the presence of a third factor
Effect Modifier
Comparing the odds of exposure among the cases to the odds of exposure among the controls.
a*d/b*c
Exposure Odds Ratio
the immunity of a group or population; resistance of a population to a specific disease or agent based on the resistance to infection of a high proportion of individuals members of the population
Herd Immunity
Maternal obesity is associated with increased risk of neonatal death. To investigate this association, data from the US National Maternal and Infant Health Survey were used. Only information on mothers with infant deaths and live births were included in this analysis. Self-reported pre-pregnancy BMI and weight gain were used for the exposure measures. Compared with normal weight women, obese women had increased risk of infant death.
Case control from a Cross-sectional survey
Key Elements: aggregate data, rates or prevalence of disease in an area, rates or prevalence of exposure in an area, analyzed as correlations or scatterplots
Sources of Bias: ecological fallacy, poor quality or incomplete information (as investigator is dependent on available data)
Ecological Study
concerns the estimate of association in the sampled population. Results from accurate measurement and estimation and valid inferences – apart from random error.
Internal Validity
A measure of how often a particular event happens in one group compared to how often it happens in another group, over time.
What are Hazard Ratios
The spectrum of disease/stages of disease - full range of the manifestations of a disease
Preclinical, subclinical, clinical, and latent