ClinEpi

Question 1

confounding bias

Answer 1

a distortion in the results due to a mixing of the effects of exposure with the effects of some third, extraneous, factor. Confounding occurs when some third factor is associated with both the exposure and the disease

Question 2

ways to prevent confounding variables

Answer 2

randomization, matching subjects based on confounding, restriction

Question 3

selection bias

Answer 3

a distortion in the results due to a difference between subjects who participated in a study and those who are theoretically eligible but did not participate (i.e., the source population).

Question 4

three ways for selection bias to occur

Answer 4

1. the way they are selected
2. refusal to participate
3. withdrawal or loss to follow up

Question 5

measurement bias

Answer 5

a distortion in the results (e.g., the relative risk for the association between an exposure and a disease) due to error in measurement of the exposure, or measurement of the disease, or both

Question 6

nondifferential measurement bias

Answer 6

occurs when errors in the measurement of exposure (second hand smoke) are independent of the disease (sinusitis), or when the errors in the measurement of disease (sinusitis) are independent of exposure

usually bias towards the null

Question 7

differential measurement bias

Answer 7

occurs when errors in measurement of exposure depend on the disease, or when errors in measurement of disease depend on the exposure. If persons who had sinusitis were less (or more) likely to under-report exposure to second hand smoke than persons without sinusitis, then there would be differential measurement bias of exposure

can produce bias towards null or away from null

Question 8

cross sectional studies

Answer 8

examines presence or absence of disease and presence or absence of an exposure…cannot draw conclusions on cause/effect

Question 9

descriptive studies

Answer 9

describe frequency, early signs, natural history and determinants of a disease

no control groups

Question 10

cohort studies

Answer 10

watch from exposure to outcome

Question 11

case control studies

Answer 11

watch from outcome to exposure \, control should be similar in all aspects except not have the same outcome

Question 12

randomized controlled trials

Answer 12

gold standard, only way to eliminate selection and confounding biases

Question 13

analytical studies

Answer 13

have a control group