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Flashcards in Bias and Misclassification Deck (37):


A systematic ( non-random) error in study design or conduct leading to errounous results....distorts the relationship btw exposure and outcome



A source of error for assesing internal validity


What can be done to fix a bias

Nothing after the study has ended, bc it has already occured. ANy consideration must be done before hand.


What 3 components do researchers look for when assesing for a bias?

Sourse, type... magnitude, strength... direction

for magnitutde can account entirely for wk association, but not likely to acount for entire very strong association... Large OR/RR


The direction of a bias

can over or under estimate the true measure of association


Information/observation/ measurement related

Any aspect in the way the researcher collects inforamtion or measure/observes subject which creates systematic differences btw groups in the quality/accuracy of their information


Selection related bias

any aspect in the way the reasearcher selects subjects which creates a systemeat difference in the composition btw groups.... not reprenting the full population... P value tell if groups are equal


Selection bias

Selecting study subjects that are not representative of your primary population of interest or that generates differences in groups being compared


Healthy worker bias

can easily be seen in prospective cohort studies... workers usually exhibit lower overall death rates than the general pop bc severly ill and disablesd ppl ar eexcluded form employment


Self-Selection/ Participant (responder) Bias

those that wish to participate(volunteer) may be differnt in some way to those that don't bolunteer or self-select(refusal/non repsonse) to partcipate


Control selection bias

can easily be see in case control studies
It's hard to find controls. they have to be as close as possible without ever having disease.


Recall Bias

A differential level of accuracy in provided information btw study groups. People who have had a bad experience have a much clearer memory of detail


Hawthorne effect

The nobelty of being research subjects and the increased attention from such coudl lead to temporary increases in study examples responses


Can loss to followup happen in a cohort study?

Yes if it is prosepective


Contamination bias

interventional study.... members of the control gourp accidently or outside of the study protocol receive the treatemnt or are exposed to the intervention being studided


compliance bias

interventional studies, groups being interventinoally studdied have difference compliences


lost to followup bias

groups being studied have different withdrawal or lost to followup rates or there are other differences btw those that stay in the study and those that withdraw or are lost to fllow up
differential vs not differential


What are selection related biases?

healthy worker biasas, self selection bias, control selection bias


What are subject related variation?

Recall, contamination bias, complaince bias, lost to followup bias,


What are observer related variation?

Interviewer, diagnosis/surveillance,


interview bias

a systematic difference in soliciting, recording or interpreting on the part of the reasearcher, interviewers knowledge may influence response, and not apply equally btw groups. why a double blind study is good


diagnosis/surveillance(expectation) bias

different evaluation/classification/diagnosis/observation btw study groups. observer may have preconceived expectiations of what they should find... hawthorne like effect for researchers perspective


kappa statistic

allows statistics to be done on evaluators to see if there is any differene btw them.


Controlling for bias

Select most precise, accurate, medically-appropriate measures of assessment and evalution/observation... used published and past utilized techniques and process if possible


ways to control for bias

blinding/masking, randomly allocate observers/interviewers for data collection, build in as many methods necessart ro minimize loss to followup, start with more people then needed for loss to follwo up


Misclassification Bias

error in classifying either disease or exposure status or both... putting ppl in the wrong box



error in both groups equal.... Misclassification of exposure or disease which is unrelated to the other, depending on study design


non-differential effect

For dichotomous 2 category variables, bias can move the measure of association TOWARD THE NULL HYPOTHESIS..... MOVES IT TOWARD 1.0... conservatie error



misclassification of exposure or disease is related to the other, depending on study design


differential effect

bias can move the measure of association IN EITHER direction... it can inflate or attenuate your effect... differntial is related to the opposite element


I unknowingly misclassified 10 cases of exposure in ONLY the cases

this is differential, bc it only effected the one side,


There is a misclassification on both sides, but not in equal amounts. 10% on one side, 40% on other

this is differential, bc they are not balanced... still shifting the measurements unequally


Misclassified both groups by the same amount

non differential... pushes the OR towards nutrality, and more likely for us to say there is no difference so the error is conservative and less painful


Controlling for misclassifications

same as information bias


Neyman bias

fatal cases being excluded, only looking at the living.


Lead-time bias

amount of time a person has to see the disease present, cancer vs strep throat


length bias