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Flashcards in Bias, Sample Collection & Confounding Deck (27)
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1

Any systematic error in an epidemiology study that results in an incorrect estimate of the association btwn exposure & risk of dz.

Bias

2

List 2 broad types of bias

  • Selection bias
  • Information bias

3

List the different types of selection bias.

(3)

  • Surveillance bias
  • Non-response bias
  • Inapproriate comparison group

4

When does surveillance bias occur?

animals are more closely followed by clinicians b/c are these animals are predisposed to a particular dz.

5

What happens in inappropriate comparison group?

 

Control does not appropriately represent the population from which cases arose

6

How can we avoid Selection Bias?

  • randomly select subjects
  • high response rates
  • low withdraw rates

7

List the 5 different types of Information Bias.

  • Interviewer bias
  • Recall bias
  • Incomplete medical record use
  • Misclassifcation bias
  • Observer bias

8

What happens in interviewer bias?

Interviewer asks questions in such a manner that affects subjects' response

(leading questions, etc)

9

What happens in Recall Bias?

  • Subjects don't accurately remember exposure
  • Family members provide info on subject

10

What happens in Misclassifaction bias?

  • Inaccurate data collection leads exposure or disease to be misclassified.
  • Case as control, control as case

11

When does Interobserver variation of Observer Bias occur?

  • >2 observers
  • variation btwn those reading or interpreting results

12

When does Intraobservation variation of Observer Bias occur?

  • 1 observer
  • variation btwn 2 observations made by 1 person

(think about interpretation of radiographs, experienced vs. novice)

13

How can we control bias?

  • Careful study design
  • Good data collection
    • blindness
    • well trained personnel
    • multiple sources of data

14

Best method of sampling?

Random sampling

15

Method characteristics:

  • each subject  in a population has equal chance of being selected
  • computer programs

simple random sampling

16

Method characteristics:

  • selection has a known & equal chance of being selected

Systematic Random sampling

17

Samples are divided into strata & a random sample taken from each strata

Stratified Random Sampling

18

Selection of samples in space & time

Cluster sampling

19

Pro's & Con's of Non-random Sampling

 

  • Pro: practical

 

  • Con: produces bias (can't quantify)

20

List the 3 types of Non-random Sampling

  • Convenience sampling
  • Purposive sampling
  • Haphazard sampling

21

The distortion or masking of an association btwn exposure & a Dz. b/c of a 3rd factor.

Confounding

22

Confouding variable/factor?

  • BE an independent risk factor for the dz.
  • ASSOCIATED w/ exposure (risk) but not a result of the risk of interest

23

How can we control confounding?

Study Design

  • Randomization
  • Matching
  • Restriction

24

Strength of randomized control trails?

(in regards to confounding)

they control for known & UNKNOWN confounders

25

Subjects selected via matching allow confounders to be ______ ______ among the case & control groups.

 

evenly distributed

26

How does restriction help prevent confounding?

restricts study to a subgroup that is homogenous for the possible confounder; helps elminate

27

Examples of confounding variables?

  • Sex
  • Breed
  • Age