Biostats

Question 1

Accumulation effect

Answer 1

Risk associated w duration of exposure: mom cumulative exp necessary for exp to have a significant effect on risk

Question 2

Lead time bias

Answer 2

Dx of a disease at an earlier stage = prolongs survival BUT inc survival time d/t early detection

Question 3

Observer bias

Answer 3

Misclassification of data d/t individual diff or preconceived expectations

Reduced by:

1. Double-blind study
2. Multiple observers encode n verify

Question 4

Attrition bias

Answer 4

Form of selection bias

unequal loss of participants from a randomized controlled trial (RCT).

Question 4

Allocation vs selection bias

Answer 4

Allocation = pts nonrandomy assigned to tx and control grps

Selection = pts not representative of the intended population. eg only cancer pts enrolling in a experimental trial

Question 5

Referral / admission rate bias

Answer 5

Eg hospital specializing in treating asbestos may report inc relation bw asbestosis and lung ca

Question 7

Length-time bias

Answer 7

rapidly progressing diseases are less likely to be detected

Question 8

Length time vs Lead time bias

Answer 8

Length time bias: rapidly progressing diseases less likely to be detected

Lead-time bias: screening leads to inc detection

Question 9

Detection bias

Answer 9

Pts w RF (eg. Smoking) undergo more testing/ screening

Question 11

Preventing bias

Answer 11

1. Double blind studies
2. Randomized
3. Placebo
4. Cross-over studies

Question 12

Case-control

Answer 12

Measures exposure status

Control - Normal grp

Question 13

Study designs

Past:

Present:

Future:

Answer 13

Past:

1. Retrospective cohort : incidence, RF
2. Case-control: RF frequency, OR

Present:
1. Cross-sectional: Prevalence

Future:

1. Prospective cohort: RF, incidence
2. Clinical trial: Tx + control, outcome of interest

Question 20

How is confounding controlled in case-control?

Answer 20

Matching

Question 23

Cross-sectional study

Answer 23

Prevalence study

Exposure and outcome

Question 24

Errors

α error:

β error:

1-β:

Answer 24

α error: FP
p<0.05

β error: FN
β = 0.2

1-β: Power = 80%

Question 25

Prospective cohort

Answer 25

Exposed group followed over time for dev of disease

Question 27

OR calculated in?

Answer 27

CohORt (uw)

Case-control (FA)

Question 28

Prevalence calculated in

Answer 28

Cross-sectional

Question 29

RR calculated in

Answer 29

Cohort

Question 30

Precision vs accuracy

Answer 30

Precise = how close together it is

Accuracy = how close to the target value

Question 31

RCT

Answer 31

Compares Tx

Drug vs placebo

Question 32

Cumulative incidence

Answer 32

New cases/ total people at risk @ a specific time

Question 33

ARP

Answer 33

ARPexposed = 100 × [(risk in exposed – risk in unexposed)/risk in exposed]

ARP = (RR-1)RR X 100

Question 34

How is the accuracy of screening tests determined?

Answer 34

Area under curve (AUC) of receiver operating characteristic (ROC) ~ 1 w/ high SN + SP

Question 35

Test used to compare means of groups

Answer 35

ANOVA >3 grp

Question 36

Test used to determines association bw 2 variables

Answer 36

Chi-square

Question 37

Test used to compare means of 2 groups

Answer 37

T-test

Question 38

Test used to determine the relationship bw 2 variables

Answer 38

Correlation coefficient