Equations

Question 1

In a two by two table, what is on the top and what is on the side.

Answer 1

top, x = disease = the d

side, y = test or exposure

Question 2

Starting from the top left to the bottom right, what is the order of true positives and true negatives in a 2x2 table?

Answer 2

TP, FP
FN, TN
=
a,b
c,d

Question 3

Sensitivity equation and blank rate

Answer 3

a/a+c

true positive rate

snaac

Question 4

Specificity equation and blank rate

Answer 4

d/d+b

true negative rate

Question 5

Positive predictive value

Answer 5

a/a+b

Question 6

Negative predictive value

Answer 6

d/d+c

Question 7

Odds ratio equation and used in what type of study? Mnemonic?

Answer 7

a/c
—– = ad/bc
b/d

Or add because

used in case-control studies

Question 8

Odds ratio interpretation/ used in what type of study?

Answer 8

OR > 1 Means that exposure is associated with higher odds of the outcome

OR < 1 Means that exposure is associated with lower odds of the outcome

OR = 1 means No difference between exposure and Outcome

Used in case control studies

Question 9

Relative risk equation and used in what type of study?

Answer 9

c/c+d

Used in cohort studies

Question 10

Relative risk meaning: RR < > & =

Answer 10

RR>1 Means increased risk of outcome

RR<1 Means decreased risk of outcome

RR=1 Means no risk of of outcome

Question 11

Relative risk reduction

Answer 11

1 - relative risk

=

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

Question 12

Absolute risk = probability of an event ____/ given ____ period

Answer 12

probability of an event occurring/ given time period

Question 13

Absolute risk reduction

Answer 13

c/c+d - a/a+b

Question 14

Number needed to treat

Answer 14

1/absolute risk reduction

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

Question 15

Attributable risk/ Absolute risk increase

Answer 15

a/a+b - c/c+d

Question 16

Number needed to harm

Answer 16

1/attributable risk

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

Question 17

Incidence

Answer 17

            population at risk

Question 18

Prevalence

Answer 18

population at risk

Question 19

Positive likelihood ratio

Answer 19

sensitivity/ 1 - specificity –> ((a/a+c)/(1 - d/d+b))

=

non diseased people with a + test result

Question 20

Negative likelihood ratio

Answer 20

1 - sensitivity/ specificity –> ((1 - a/a+c)/(d/d+b))

=

non diseased people with a - test result

Question 21

Hazard ratio =

when are Hazard ratios used? What are they similar to?

Answer 21

Hazard in the control group

Hazard ratios are interpreted similarly to relative risk and are used in cohort studies. You use confidence intervals to interpret them. A confidence interval that includes one is not statistically significant.

Question 22

Interpret a hazard ratio of .5, 1, 2

Answer 22

Hazard in intervention group
HR= —————————————————–
Hazard in control group

HR = 0.5: at any particular time, half as many patients in the treatment group are experiencing an event compared to the control group.

HR = 1: at any particular time, event rates are the same in both groups,

HR = 2: at any particular time, twice as many patients in the treatment group are experiencing an event compared to the control group.

Question 23

Attack rate =

Answer 23

total population at risk

Question 24

What is a foodborne attack rate

Answer 24

A food-specific attack rate is the number of persons who ate a specified food and became ill divided by the total number of persons who ate that food

Question 25

Define positive likelihood ratio in words

Answer 25

Ratio representing the likelihood of having the disease given a positive test result

Question 26

Negative likelihood ratio, define in words

Answer 26

Ratio representing the likelihood of having a disease given a negative result

Question 27

Give the three percents associated with 1, 2, and 3 standard deviations away from the mean

Answer 27

68

95

99.7