EXAM 1 IMPORTANT DEFINITIONS

Question 1

Define sensitvity

Answer 1

Probability that subject D+ tests +ve

Question 2

Define specificity

Answer 2

Probability D- tests -ve

Question 3

Define apparent prevalence

Answer 3

Proportion of +ve subjects

Question 4

Define true prevalence

Answer 4

Proportion of subjects w/ known infection
(D+ total)

Question 5

Define Positive predictive value

Answer 5

Proportion that subject is T+ and D+

Question 6

Define Negative predictive value

Answer 6

Proportion that subject is D- and T-

Question 7

Formula for sensitivity

Answer 7

a/(a+c)

Question 8

Formula for specificity

Answer 8

d/(b+d)

Question 9

Formula for apparent prevalence

Answer 9

(a+b)/n

Question 10

Formula for true prevalence

Answer 10

(a+c)/n

Question 11

Formula for PPV

Answer 11

a/(a+b)

Question 12

Formula for NPV

Answer 12

d/(c+d)

Question 13

List the 5 phases of an epidemic curve

Answer 13

1) endemic level
2) threshold level
3)ascending phase
4)plateau/culminating phase
5) descending phase

Question 14

Describe the endemic level of an epidemic curve

Answer 14

expected level of disease, high herd immunity, most individuals are carriers, no obvious new carriers, high source of infection

Question 15

Describe the threshold level

Answer 15

pre-epidemic pd, herd immunity declined

Question 16

Describe the ascending phase

Answer 16

reduced herd immunity, # of diseased individuals increases, slope depends on pop density and exposure type, high intensity/source of infection

Question 17

Describe the plateau/culminating phase

Answer 17

depends on availability of susceptible individuals, max # of new cases, herd immunity rises

Question 18

Describe the descending phase

Answer 18

new cases decreases, herd immunity increases, sick individuals may recover, sensitive individuals die, immunity can happen, infection source decreases

Question 19

Define cumulative incidence rate

Answer 19

Fraction of initially susceptible individuals in a population who become new cases during a specific follow-up period

Question 20

Formula for cumulative incidence rate

Answer 20

new cases during a specified period/ avg # individuals at risk

Question 21

Define cumulative incidence

Answer 21

Indication of avg risk, only for first occurrence of disease

Question 22

Define incidence density rate

Answer 22

of new cases of disease that occur per unit of individual time at risk in a defined period

Question 23

Formula for incidence density rate

Answer 23

new cases during specific pd/ sum of person-years at risk periods

Question 24

crude mortality rate formula

Answer 24

Total # deaths/ avg population

Question 25

Cause-specific mortality rate

Answer 25

deaths from a particular disease/ avg population at risk during time pd

Question 26

Formula for proportional mortality rate

Answer 26

Deaths of disease y/ total deaths

Question 27

Case fatality rate definition

Answer 27

Death among individuals who develop the disease

Question 28

Formula for case fatality rate

Answer 28

deaths from disease y/ cases of disease y