Module 2 and 3

Question 1

what is the formula for incidence rate (IR)?

Answer 1

IR = # NEW cases during time period /
Total person-time of observation in population at risk

person time is number of years (day, etc) contributed by each person

Question 2

what does incidence rate mean?

Answer 2

It measures how fast new cases in study population are occurring

Question 3

what is the formula for cumulative incidence (CI)?

Answer 3

CI = # NEW cases during time period /
# in population at risk at start of time period

Question 4

what does the cumulative incidence value mean?

Answer 4

Estimate of how many people will get the disease in a certain population

Question 5

If 60 cases of menegitis were reported over 2 years in a population of 100,000 people, what is the incidence rate of this disease?

Answer 5

IR = 30/100,000 or 60/200,000

need to multiply people x years to get person-years

Question 6

Out of a workplace with 200 employees, 10 employees got Shingles on April 30. On May 18, 6 more employees came down with Shingles. What was the cumulative incidence for May?

Answer 6

cumulative incidence = 6/190

the denominator can only include people who were still at risk (i.e.: did not have disease) at the beginning of the month being examined

Question 7

What is an attack rate? what is its formula?

Answer 7

Attack rates are a type of cumulative incidence used in outbreaks or pandemics

CI = # NEW cases over the course of outbreak /
# in population at risk at start of outbreak

Question 8

Is cumulative incidence a rate or a proportion? Is time in the denominator?

Answer 8

Cumulative incidence is a proportion. Time is not in denominator.

Question 9

Is incidence rate a rate or proportion? Is time in the denominator?

Answer 9

Incidence rate is a rate. Person-time at risk is in denominator.

Person-time is accurred until there is a change (disease, death, cured)

Question 9

Prevalence is __________

Answer 9

the proportion of disease among the population

Question 10

what is the formula for prevalence, if population is steady and incidence rate/duration stay the same?

Answer 10

P / (1 - P) = IR x D

IR = incidence rate, D = duration of disease

Question 11

what is the formula for prevalence if the incidence is rare?

Answer 11

P = IR x D

IR = incidence rate, d = duration of disease

Question 12

If a disease occurs more or less often in a group with an exposure, then there is an ________ between the exposure and disease.

Answer 12

If a disease occurs more or less often in a group with an exposure, then there is an association (relationship) between the exposure and disease.

Question 13

Risk difference is an ____________ of association

Answer 13

Risk difference is an absolute measure of association

Question 14

Risk ratio is a …. measure of association

Answer 14

Risk ratio is a relative measure of association

Question 15

Risk Difference (RD):
1. calculates the difference between 2 measures of disease frequency
OR
2. calculates the ratio between 2 measures of disease frequency

Answer 15

Risk difference calculates the difference between 2 measures of disease frequency

Question 16

what represents the measure of public health impact of exposure on disease occurrence?

Answer 16

Absolute measure/risk difference

also, incidence rate difference, cumulative incidence difference, and prevalence difference

Question 17

what represents measure of strength or magnitude of the association between an exposure and a disease?

Answer 17

Relative measure/risk ratio

also, rate ratio, relative risk, other things ending in ratio

Question 18

What measures the excess rate of disease due to expsoure?

Answer 18

Risk difference

Question 19

what measures the strength of association between the exposure and disease?

Answer 19

Risk Ratio/Rate Ratio

Question 20

What is the formula for Risk Difference?

Answer 20

RD = Re - Ru

Question 21

What is the formula for Risk Ratio/Rate Ratio?

Answer 21

RR = Re/Ru

Question 22

An epidemiology study was carried out with 3000 participants. Of those, 750 were exposed to the risk factor that was being studied and 570 of those had the disease of interest. Of the people who were not exposed, 675 had the disease of interest. Calculate the risk difference (RD) per 1000 people for the exposed and unexposed groups.

Answer 22

460 cases per 1000 people

Question 23

A smoking-cancer study was carried out with 3000 participants. Of those, 750 were exposed to the cigarette smoke and 570 of those had cancer. Of the people who were not exposed to cigarette smoke, 675 had cancer. Calculate the risk ratio (RR) per 1000 people for the exposed and unexposed groups.

Answer 23

2.5

Question 24

The excess number of cases in the total population due to exposure is the ...

Answer 24

Population Risk Difference (PRD)

Question 25

The Population Risk Difference identifies..

Answer 25

PRD identifies the number of cases that would be eliminated in the total population if the exposure (in Re) were eliminated or reduced to the levels in the Ru group.

Question 26

If you know the Rt (incidence rate in total pop) and Ru (rate in unexp), what formula do you use to find Population Risk Difference?

Answer 26

PRD = Rt - Ru

Question 27

If you know the Risk Difference and the Pe (prevalence of disease in population in exposed), what is the best formula for the population risk difference? | Pe will probably look like a percentage

Answer 27

PRD = RD x Pe

Question 28

What is the proportion of the disease among the exposed that would be eliminated if the exposure was eliminated?

Answer 28

Attributable proportion of the exposed

Question 29

What is the proportion of the disease among the total population that would be eliminated if the exposure was eliminated?

Answer 29

Attributable proportion among the total population

Question 30

For absolute measures like incidence rate, what is the formula for the Attributable proporation of the exposed?

Answer 30

APe = (Re - Ru) /Re x 100

Question 31

Consider the following data related to asthma and pnuemonia deaths: Death rate from pnuemonia in people with asthma: 5/1,000/year Death rate from pnuemonia in people without asthma: 0.5/1,000/year Prevalence of asthma in population: 30% Calculate the Attributable Proportion (%) among the exposed of CVD and fill that in here (round up to one decimal point): Ape =

Answer 31

APe = 90 % ## Footnote The prevalence is irrelevant in this question

Question 32

For absolute measures like incidence rate, what is the formula for the Attributable proportion among the total population?

Answer 32

APt = (Rt-Ru) / Rt x 100

Question 33

Consider the following data: Total population of a state has **incidence rate** of weird rashes = 20/1,000/year The city with the lowest rate of spider bites has an incidence of weird rashes = 0.05/1,000/year Calculate the Attributable Proportion (%) among the total population and fill that in here (round up to one decimal point): APt =

Answer 33

APt = 100% | 99.75% rounded up

Question 34

What is the Preventative Fraction?

Answer 34

If an exposure is considered protective against the disease, you would calculate the preventative fraction (PF) which is the proportion protected against disease because of exposure.

Question 35

What is the formula for the preventative fraction?

Answer 35

PF = (Ru - Re) / Ru x 100

Question 36

Families who put their babies in car seats had an incidence of 12 babies injured per 1000 car crashes. Families who did not use car seats had an incidence of 50 babies injured per 1000 car crashes. What is the preventative fraction of car seat usage?

Answer 36

76%

Question 37

If there is no association between the exposure and disease, the Relative Risk will be..

Answer 37

the Relative Risk will be 1.0

Question 38

If there is a positive association between the exposure and disease, the Relative Risk will be...

Answer 38

the Relative Risk will be greater than 1.0

Question 39

If the exposure prevents disease, the Relative Risk will be...

Answer 39

The Relative Risk will be less than 1.0

Question 40

Express the relative risk as a percentage

Answer 40

(RR - 1) x 100 = RR%

Question 41

For relative measures like Risk Ratio, what is the formula for Attributable Proportion among the exposed?

Answer 41

APe = (RR - 1) / RR x 100

Question 42

If the Relative Risk is 3.2, what is the APe?

Answer 42

(3.2 - 1)/3.2 = 69% | 68.75% rounded up

Question 43

For relative measures like relative risk, what is the formula for the attributable proportion among the total population?

Answer 43

APt = (Pe (RR - 1)/(Pe (RR-1) +1)) x 100

Question 44

If the relative risk is 4.5 and the prevalence of the disease is 50% what is the APt?

Answer 44

64% | rounded from 63.6%

Question 45

Why do you do direct age standardization?

Answer 45

You use direct age standardization, so that rates of disease various population can be compared. Without standardization, a population may appear to have a higher death rate in an age group simply because more of their population is in that age range.

Question 46

What 2 pieces of information are needed for direct age standardization?

Answer 46

1. Age-specific rates in each group (such as state, county) 2. Age structure of a standardized population (US rates for states and counties, World rates for countries)

Question 47

how do you calculate the direct age standardization for a region?

Answer 47

You multiply the local rate (proportion) for the age group by the percentage the represents in the standardized population. You do that for each age group and then add up all numerators to get the age standardized rate for the region.