Module 2 and 3 Flashcards
what is the formula for incidence rate (IR)?
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
what does incidence rate mean?
It measures how fast new cases in study population are occurring
what is the formula for cumulative incidence (CI)?
CI = # NEW cases during time period /
# in population at risk at start of time period
what does the cumulative incidence value mean?
Estimate of how many people will get the disease in a certain population
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?
IR = 30/100,000 or 60/200,000
need to multiply people x years to get person-years
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?
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
What is an attack rate? what is its formula?
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
Is cumulative incidence a rate or a proportion? Is time in the denominator?
Cumulative incidence is a proportion. Time is not in denominator.
Is incidence rate a rate or proportion? Is time in the denominator?
Incidence rate is a rate. Person-time at risk is in denominator.
Person-time is accurred until there is a change (disease, death, cured)
Prevalence is __________
the proportion of disease among the population
what is the formula for prevalence, if population is steady and incidence rate/duration stay the same?
P / (1 - P) = IR x D
IR = incidence rate, D = duration of disease
what is the formula for prevalence if the incidence is rare?
P = IR x D
IR = incidence rate, d = duration of disease
If a disease occurs more or less often in a group with an exposure, then there is an ________ between the exposure and disease.
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.
Risk difference is an ____________ of association
Risk difference is an absolute measure of association
Risk ratio is a …. measure of association
Risk ratio is a relative measure of association
Risk Difference (RD):
1. calculates the difference between 2 measures of disease frequency
OR
2. calculates the ratio between 2 measures of disease frequency
Risk difference calculates the difference between 2 measures of disease frequency
what represents the measure of public health impact of exposure on disease occurrence?
Absolute measure/risk difference
also, incidence rate difference, cumulative incidence difference, and prevalence difference
what represents measure of strength or magnitude of the association between an exposure and a disease?
Relative measure/risk ratio
also, rate ratio, relative risk, other things ending in ratio
What measures the excess rate of disease due to expsoure?
Risk difference
what measures the strength of association between the exposure and disease?
Risk Ratio/Rate Ratio
What is the formula for Risk Difference?
RD = Re - Ru
What is the formula for Risk Ratio/Rate Ratio?
RR = Re/Ru
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.
460 cases per 1000 people
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.
2.5
The excess number of cases in the total population due to exposure is the …
Population Risk Difference (PRD)
The Population Risk Difference identifies..
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.
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?
PRD = Rt - Ru
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
PRD = RD x Pe
What is the proportion of the disease among the exposed that would be eliminated if the exposure was eliminated?
Attributable proportion of the exposed
What is the proportion of the disease among the total population that would be eliminated if the exposure was eliminated?
Attributable proportion among the total population
For absolute measures like incidence rate, what is the formula for the Attributable proporation of the exposed?
APe = (Re - Ru) /Re x 100
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 =
APe = 90 %
The prevalence is irrelevant in this question
For absolute measures like incidence rate, what is the formula for the Attributable proportion among the total population?
APt = (Rt-Ru) / Rt x 100
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 =
APt = 100%
99.75% rounded up
What is the Preventative Fraction?
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.
What is the formula for the preventative fraction?
PF = (Ru - Re) / Ru x 100
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?
76%
If there is no association between the exposure and disease, the Relative Risk will be..
the Relative Risk will be 1.0
If there is a positive association between the exposure and disease, the Relative Risk will be…
the Relative Risk will be greater than 1.0
If the exposure prevents disease, the Relative Risk will be…
The Relative Risk will be less than 1.0
Express the relative risk as a percentage
(RR - 1) x 100 = RR%
For relative measures like Risk Ratio, what is the formula for Attributable Proportion among the exposed?
APe = (RR - 1) / RR x 100
If the Relative Risk is 3.2, what is the APe?
(3.2 - 1)/3.2 = 69%
68.75% rounded up
For relative measures like relative risk, what is the formula for the attributable proportion among the total population?
APt = (Pe (RR - 1)/(Pe (RR-1) +1)) x 100
If the relative risk is 4.5 and the prevalence of the disease is 50% what is the APt?
64%
rounded from 63.6%
Why do you do direct age standardization?
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.
What 2 pieces of information are needed for direct age standardization?
- Age-specific rates in each group (such as state, county)
- Age structure of a standardized population (US rates for states and counties, World rates for countries)
how do you calculate the direct age standardization for a region?
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.
