Study Design Flashcards
Observational Studies
Descriptibe, analytical, ecological or correlational, cross-sectional, case-control, cohort,
Experimental Studies
Randomized controlled trials, Cluster randomized control trials, field trials, community trials
Descriptive Studies
limited to the description of the occurrence of a disease in a population and is often the first step in an epidemiological investigation.
Analytical Studies
Further by analyzing relationships between health status and other variables.
Ecological or Correlational Studies
Used for generating hypotheses
Data can be used from different populations with widely different characteristics or extracted from different data sources.
Cross-sectional (Prevalence)
Measure of the prevalence of disease
Measurements of exposure and effect are measured simultaneously
Case-control (Retrospective)
Include people with a disease of interest and a suitable control group of people unaffected by the disease or outcome variable.
Include people with a disease of interest and a suitable control group of people unaffected by the disease or outcome variable.
Investigators collect data on disease occurrence at one point in time and exposures in a previous point in time.
Odds Ratio
The association of an exposure and a disease in a case-control study is measured by calculating the odds ration which is the ratio of the odds of exposure among the cases to the odds of exposure among the controls.
Cohort (Follow-up, or incidence)
Variables of interest are specified and measured and the whole cohort is followed up to see how the subsequent development of new cases of the disease differs between the groups with and without
Provide the best information about the causation of disease and the most direct measurement of the risk of developing disease.
Randomized Controlled Trials
Patients = subjects, particular intervention, randomly allocated subjects, any differences are chance occurrences unaffected by conscious or unconscious biases of the investigators
Field Trials
participants are healthy, assumed to be at risk, data obtained from non-institutionalized people in the general pop., purpose to prevent disease, and used to evaluate interventions
Community Trials
Participants are the community, appropriate for diseases that are influenced by social conditions and for which prevention efforts target group behaviour
Ecological Fallacy
Occurs because the association observed between variables at the group level does not necessarily represent the association that exists at the individual level.
Limits of Community Trials
§ Other methods are required to ensure that any differences found at the end of the study can be attributed to the intervention rather than to inherent differences between communities.
Only a small number of communities can be included and random allocation is usually not practicable.
Random Error
Value of the sample measurement diverges - due to chance alone- from that of the true population value.
Random error causes inaccurate measures of association.
Sampling Error
Caused by the fact that a small sample is not representative of all the populations variables.
Measurement Error
Reduced by stringent protocols, and by making individual measurements as precise as possible
Systematic Error
Occurs in epidemiology when results differ in a systematic matter from the true values.
Selection Bias
Occurs when there is a difference between characteristics of the people selected for the study and the characteristics of those who are not. i.e., self-selected
Measurement Bias
Occurs when the individual measurements or classifications of disease are inaccurate.
Confounding
Confounding occurs when the effects of two exposures have not been separated and the analysis concludes that the effect is due to one variable rather than the other.
How to control confounding
Randomization of variables, restriction of participants characteristics, distribution confounding variables equally, and control should be done in the analytical phase rather than design
Stratification
Stratification involves the measurement of the strength of associations in well defined and homogenous categories of the confounding variable.
Internal Validity
Degree to which the results of an observation are correct for the particular group of people being studies.
External Validity
Extent to which the results of a study apply to people not in it
Informed Consent
Free and voluntary MUST be obtained and they have the right to withdrawal anytime
Confidentiality
Obligation to preserve confidentiality of information they obtain in their studies.
Ethical Principles
informed consent, confidentiality, respect for human rights, scientific integrity
