Biostats

Question 1

Cross-sectional study

Answer 1

snapshot of a population
frequency of a disease and frequency of risk-related factors are assessed in the present
Measures prevalence

Question 2

Case-control study

Answer 2

compares a group of people with disease to a group without disease
Measures odds ratio

Question 3

Cohort study

Answer 3

compares a group with a given exposure or risk factor to a group without such exposure
Measures relative risk

Question 4

What is the formula for sensitivity?

Answer 4

a/a+c

Question 5

What is the formula for specificity?

Answer 5

d/b+d

Question 6

What is the formula for PPV?

Answer 6

a/a+b

Question 7

What is the formula for NPV?

Answer 7

d/c+d

Question 8

What is the formula for odds ratio?

Answer 8

(a/b)/(c/d)

Question 9

What is the formula for relative risk?

Answer 9

(a/a+b)/(c/c+d)

Question 10

What is the formula for attributable risk?

Answer 10

(a/a+b) - (c/c+d)

Question 11

What is the formula for absolute risk reduction?

Answer 11

ARR = (c/c+d) - (a/a+b)

Question 12

What is the formula for NNT?

Answer 12

1/ARR

Question 13

What is the formula for NNH?

Answer 13

1/AR

Question 14

What is the formula for relative risk reduction?

Answer 14

RRR = 1 - RR

Question 15

What is the formula for incidence?

Answer 15

incidence rate = # of new cases/# of people at risk

Question 16

What is the formula for prevalence?

Answer 16

prevalence = # of existing cases/total # of people in population

Question 17

Study X shows that VitC can prevent coronavirus infections, but 10 other studies show no benefit. What type of error is found in study X?

Answer 17

type 1 error (alpha error); false positive

Question 18

Study Y shows that aspirin administration during an MI offers no improvement in patient morbidity or mortality. What type of error is present?

Answer 18

Type II error (beta error); false negative

Question 19

What are the differences between mean, median, and mode?

Answer 19

mean = average
median = middle
mode = most common result

Question 20

What does it mean to say that a statistical distribution has a positive skew?

Answer 20

positive skew = bigger tail to right side of graph, but graph (hump) is shifted left
mean > median > mode

Question 21

What is attributable risk percent?

Answer 21

ARP = measure of the impact of a risk factor
ARP = 100 x [(risk in exposed-risk in unexposed)/risk in exposed]