Statistics

Question 1

Attributable risk (AR)
Or
Risk difference (RD)

Answer 1

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

Draw box
X-axis disease: + or -

Y-axis exposure:

+

or

-

+ + = a; e+ d- = b; e- d+ = c; - - = d

Question 2

Attributable risk %

Answer 2

ARx100%/[a/(a+b)]

Draw box

X-axis disease: + or -

Y-axis exposure:

+

or

-

+ + = a; e+ d- = b; e- d+ = c; - - = d

Question 3

False negative

Answer 3

1- sensitivity

Question 4

False positive

Answer 4

1 - specificity

Question 5

Cumulative incidence

Answer 5

new cases in a given time period/

Total population at risk

Question 6

Incidence rate

Answer 6

new cases of disease in a given time period/

Person-time years of observation

Question 7

Likelihood ratios (LR)

Answer 7

LR+ (positive test) =
Sensitivity/(1-specificity)

LR- (negative test) =
(1- sensitivity)/specificity

Question 8

Mortality rate, BW specific

Answer 8

deaths in specific BW categoryx1000/

# births in same BW category

Question 9

Mortality rate, fetal

Answer 9

Fetal deaths x 1000/
(Live birth + fetal deaths)

Question 10

Mortality rate, infant

Answer 10

Infant death (≤1 yo)x1000/
Live births

Question 11

Mortality rate, neonatal

Answer 11

Neonatal deaths <28d x 1000/
Live births

*Can further divide to <7d and >7d but <28d

Question 12

Mortality rate, perinatal

Answer 12

(Fetal deaths ≥ 28wk GA + neonatal deaths<7d)x1000/
(Live births+fetal deaths ≥28d GA)

Question 13

Mortality rate, postnatal

Answer 13

Postneonatal deaths (28-364d)x1000/
Live births

Question 14

NPV

Answer 14

d/(c+d) = TN/(FN+TN)

Draw box

X-axis disease: + or -

Y-axis test+:

+

or

-

+ + = a; e+ d- = b; e- d+ = c; - - = d

Question 15

NNT

Answer 15

1/(A+B)

If A = events in the control/non exposed group = c/(c+d)
B = events in the treated/exposed group = a/(a+b)

Question 16

OR aka cross product ratio

Answer 16

(axd)/(bxc)

Draw box

X-axis disease: + or -

Y-axis exposure:

+

or

-

+ + = a; e+ d- = b; e- d+ = c; - - = d

Question 17

PPV

Answer 17

a/(a+b) = TP/(TP+FP)

Draw box

X-axis disease: + or -

Y-axis test+:

+

or

-

+ + = a; e+ d- = b; e- d+ = c; - - = d

Question 18

Power

Answer 18

1- type II error

Question 19

Type I error

Answer 19

Reject null hypothesis when it is true

False positive

Question 20

Type II error

Answer 20

Do not reject null hypothesis when it is false

False negative

Question 21

Prevalance

Answer 21

= #new cases at point in time x 1000/ total population at risk

= (TP + FN)/(TP + FN + FP + TN)

Question 22

Risk ratio or relative risk

Answer 22

= AR in exposed/AR in non exposed
= [a/(a+b)]/[c/(c+d)]

Draw box

X-axis disease: + or -

Y-axis exposure:

+

or

-

+ + = a; e+ d- = b; e- d+ = c; - - = d

Question 23

Sensitivity

Answer 23

a/(a+c) = TP/(TP+FN)

Draw box

X-axis disease: + or -

Y-axis test+:

+

or

-

+ + = a; e+ d- = b; e- d+ = c; - - = d

Question 24

Specificity

Answer 24

d/(b+d) = TN/(FP+TN)

Draw box

X-axis disease: + or -

Y-axis test+:

+

or

-

+ + = a; e+ d- = b; e- d+ = c; - - = d