Biostat

Question 1

What is a case control study?

What statistical measure does it use?

Answer 1

• Compares group with dz and group without dz….looks for exposure or risk factor (retrospective)
• Odds ratio

Question 2

What’s a cohort study?

What statistical measure does it use?

Answer 2

• Group with known exposure or rf vs group without exposure…..does exposed group have higher chance of disease?
• Relative risk

Question 3

Cross sectional study?

Answer 3

Assesses FREQUENCY of disease at a particular point in time. Asks “what is happening?”

-measures disease prevalence

Question 4

Calculation for sensitivity:

Answer 4

TP / (TP +FN)

Question 5

Calculation for specificity:

Answer 5

TN / (TN + FP)

Question 6

PPV calculation:

Answer 6

TP / (TP + FP)

Question 7

NPV calculation:

Answer 7

TN / (TN + FN)

Question 8

Odds ratio is used in ____ studies. The formula is ____

Answer 8

• Case control

- AD / BC

Question 9

Relative risk is used in ____ studies. Calculation is ____

Answer 9

• Cohort studies
• ( A / (A+B) ) / ( C / (C+D) )

*risk of dev. disease in exposed group vs risk in unexposed group

Question 10

How to calculate Absolute risk reduction:

Answer 10

Risk in non-treated - risk in treated

Question 11

Calculation for NNT?

Answer 11

1 / ARR

Question 12

Calculation for # needed to harm?

Answer 12

1 / attributable risk

Question 13

Raising the cut point (increasing inclusion criteria) of a screening test increases _____ and decreases _____

Answer 13

• Increases: Specificity

- Decreases sensitivity

Question 14

What is susceptibility bias?

Answer 14

A subgroup of selection bias…Happens when the tx selection for a pt depends on the severity of their condition

Question 15

What is observer bias?

Answer 15

Observer is influenced by prior knowledge or details of the study

Question 16

What is matching?

what studies is it used in?

What does it help control?

Answer 16

• Matching participants in regards to certain confounding variables
• Case control studies
• Counfounding

Question 17

what study is best to determine incidence?

Answer 17

Cohort study

Question 18

Loss to folowup can create what kind of bias?

Answer 18

Selection bias

Question 19

WHat is respondent bias?

Answer 19

When outcome is obtained by the pt’s response rather than objective diagnostic methods

Question 20

WHat is the attributable risk percent (ARP) ?

-calculation?

Answer 20

• Etiologic fraction. Measure of the impact of a RF being studied
• ARP = (risk in exposed - risk in unexposed) / risk in exposed

OR

ARP = (RR -1 ) / RR

Question 21

Formula for +Likelihood ratio?

Answer 21

Proportion of pts with disease who test positive / pts without disease who also test positive

LR +=Sensitivity / 1 - specificity

LR- = 1 - Sen / Spec

Question 22

How to calculate pre-test odds?

Answer 22

pre-test probability / (1-pre-test probability)

AKA = prevalence / 1 - prevalence

Question 23

How to calculate post-test odds?

Answer 23

LR x Pre-test odds

Question 24

How to test Post-test probability?

Answer 24

post-test odds / (post test odds+1)