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This Concept Map, created with IHMC CmapTools, has information related to: Topic 6 bias, study dropouts are systematically differnt to those who remain in the study therefore studies should report dropout rates, symptoms but no formal diagnosis therefore may not provide a good comparison to the diagnosed group who also have symptoms, Measurement Bias 2 types are Recall Bias, healthy worker effect occurs when are not well enough to participate in a research study, people with a disease may recall differently to people without the disease thus difficult to compare between groups, particpants may inadverantly overestimate in an effort to find a reason for condition example patients with brain tumor, Measurement Bias Can be reduced by High participation rates, misclassified according to an exposure or outcome example participant who is heavy smoker is classified as a light smoker (exposure), strict and explicit criteria for what constitutes an outcome, healthy worker effect the population contains people who cannot work due to ill health, individual measurements of disease (outcome) or exposure are do not measure what they are supposed to measure, participants are likely to be healthier than the general population solution compare industry with another industry, not with general population, Selection Bias includes Attrition Bias (loss of follow up), infomation obtained from participants is not accurately recalled from the past example people with a disease may recall differently to people without the disease, healthy worker effect the population contains people who are not well enough to participate in a research study, many characteristics which differ between those who participate and those who don't people who are less likely participate usually have passive opinions, misclassified according to an exposure or outcome example Disease outcome misclassification, participant who is heavy smoker is classified as a light smoker (exposure) potential reasons participant may not have been truthful, procedures used to select participants differences in characteristics between study groups (eg in RCT), High participation rates which give a better representation of the population