Bcacp - Study Designs Exam Questions And Answers 2024.

Prospective study design begin in the present and progress forward, collecting data from subjects whose outcomes lie in the future Retrospective study design Begin and end in the present; however, this design involves a major backward look to collect information about events that occurred in the past Hierarchy of clinical study designs Internal validity in study design -validity within the confines of the study methods -does the study design adequately and appropriately test/measure what it purports? -does the student adequately and appropriate address bias, confounding, and measurement of end points? External validity in study design -validity related to generalizing the study results outside the study setting -can the results be applied to other groups, patients, or systems? -addresses issues of generalizability and representativeness Bias in study design systematic, nonrandom variation in study methodology and conductance, ultimately introducing error in outcome interpretation. Bias can occur in all aspects of the study design Selection bias an error in the selection of/sampling of individuals for a clinical study. Example: subjects chosen for the case and control groups differ in one or more characteristics that alter the outcome of the study Observational or information bias An error in the recording of individual factors of a study, such as inaccurate recording of a patient's risk factor, inaccurate recording or timing of a blood sample Recall bias Class example: studies of birth defects secondary to medications Interviewer bias: Classic example: interviews are not conducted in a uniform manner (or by the same person) for all study participants Misclassification bias Differential-the degree of outcome misclassification depends on the exposure status - a more serious problem Nondifferential- the degree of outcome misclassification is not related to exposure status Confounding in study design A variable that affects the independent or dependent variable, altering the ability to determine the true effect on the measured outcome. These factors may hide or exaggerate a true association. How to minimize confounding - all relevant information should be collected and evaluated -During the design of the study, use randomization, restriction, and matching - During analysis, use stratification, and multivariate analysis Temporality Cause before effect Strength plausibility increases with strength of relationship biological gradient dose-response relationship consistency observations for several setting specificity single cause for effect plausibility biologically plausible coherence consistency with existing knowledge analogy preclinical expectation applied to clinical testing experiment randomized controlled trials case reports/case series -document and describe experiences, novel treatments, and unusual events - allows hypothesis generation that can be tested with other study designs - reports should provide sufficient detail to allow readers to recognize same/similar cases at their practice Advantages/disadvantages to case reports/series Advantage: hypotheses can be formed, which may be the first step in describing a clinical problem - easy and inexpensive Disadvantage: does not provide explanation other than conjecture and does not establish causality or association Observational studies -Design does not involve investigator intervention, only observation. - investigate associations, not causes case-control cohort cross-sectional Case control study -Study exposure in those with and without the outcome of interest -Determine the association between exposures/risk factors and disease/condition -Retrospective -Useful to study for diseases that take long periods to develop Minimizing bias in case control studies Critical assumptions: 1. cases are selected to be representative of those who have the disease 2. Controls are represetative of the general population that does not have the disease and are as identical as possible to the cases, minus the presence of the disease 3. information is collected from cases and controls the same way Case control study advantages and disadvantages Advantages: inexpensive and can be conducted quickly. Allows investigation of several possible exposures Disadvantages: confounding must be controlled for. Observational and recall bias: looking back to recall exposures and their possible levels of exposure. Selection bias: case selection and control matching are difficult. Case control study measure of assocation Odds ratio (OR):, in some cases this can be an estimate of the relative risk (RR). The OR is interpreted as the odds of exposure to a factor in those with a condition or disease compare with those who do not have the condition or disease. Cohort Study 1. Determines the association between exposures/factors and disease/condition development. Allows an estimation of the risk of outcome (and the RR between the exposure groups). Study outcome of interest in those with and without the exposure of interest. Classic examples: Framingham CVD study Nurses Health study (oral contraceptives) 2. Describes the incidence or natural history of a disease/condition and measures it in time sequence Retrospective Cohort study advantages and disadvantages Advantages: less expensive and time consuming, no loss to follow-up, ability to investigate issues no amenable to a clinical trial, no ethical/safety issues Disadvantages: only as good as the data available, little control of confounding variable through nonstatistical approaches, recall bias Prospective or longitudinal advantages and disadvantages Advantages: Can control for confounding factors to a greater extent, easier to plan for data collection Disadvantages: more expensive and time intensive, loss of subject follow-up, difficult to study rare diseases/conditions at a reasonable cost