Terms  Definitions 

Define rate from slides in class. Give epi example. 
The changes in one quantity per unit change in another quantity. (example: incidence density)

Define ratio from slides. Give an example of one with a dimension and one without. 
A fraction where the numerator is not included in the denominator. (example w/ dimension: # of hosp. beds/1,000 people; example w/o dimension: # of epi students/ nonepi students among MPH students

What is a common epidemiological ratio? Formula? (hint: only actual measure you can get from casecontrol data) 
odds ratio
[ (# Dexp/ Not D w/exp) / (# D w/o exp / # not D w/o exp) ] 
Define prevalence ( aka prevalence proportion) and give an epidemiological example. 
The proportion of a population with a disease determined at a specific point in time.

Define odds in an epidemiological manner. 
The # of persons in a population with a disease divided by the the # of persons in a population without a disease.

Give an example of prevalence using swine flu in the berkeley school of public health. 
There are 5 cases of swine flu amongst the 200 MPH students. Thererfore PP = 5/200 = 0.025

Define incidence. Give an example. Is it a rate, ratio or proportion? 
The frequency of development of new cases of disease in a population. There was 5 cases of swine flu in 200 personyears. It is a rate.

Define cumulative incidence. 
The proportion of subjects at risk for a disease at baseline who develop the disease during a certain period of time. (ex. 20 nervous break downs per one week of finals at Berkeley)

Does cumulative incidence (CI) have a dimension? 
No bc it is a proportion and ranges from 0 to 1.

In 18 months, out of 10,000 shoppers visiting the dollar store, 25 of them come down with cleptomania due to the economic crisis. What is the CI for the 18 mo. period? 
CI = 25/10,000 = .0025 or 0.25%

Define incidence density. Give an example. 
The # of incident (aka new cases) divided the total person time. (ex.20 cases of diptheria in 8,000 person years)

What is the unit for prevalence? 
cases per persons at risk

What is the unit for an odds ratio? 
None it is dimensionless

What is the two different units for incidence density? 
# of cases per person time OR 1/ time (according to Klienbaum)

1,000 men with no history of CVD are observed for 24 months. 10 of them develop CVD on the first day of the 13th month. What is the cumulative incidence? 
CI = 10 / 10,000 = 0.001 or 0.1% per 24 months or 0.001 per 2 years.

Define crude rate. 
The # of experiences or events in a total population in certain period.

Give two common examples of crude rates. 
1. crude birth rate
2. crude death rate 
Define adjusted rate. 
A mathmatical transformation of a crude rate to account for differences in population structure (i.e. age, race, etc)

Define case fatality rate 
# of causespecific dths among cases/ # of incident cases of the same cause

Define attack rate 
# of incident cases of disease/ total population at risk over a restricted period of time

What is attack rate commonly used for? 
outbreak investigations

Is case fatality rate a rate, ratio, or proportion? 
Although is says "rate" in its name, it is actually a true proportion

What is postnatal mortality rate? 
index of the risk of death in infants aged 1 11 months

Define postneonatal mortality rate. 
# of dths in children aged 111 months / # of live births during that calendar year

What is infant mortality rate most commonly used for? 
risk of death during the first year of life

Define infant mortality rate. 
# of infant deaths in a calendar year/ # of live births during the same calendar year

Define crude birth rate. How is it expressed? 
# of live births during a given time interval / # estimated total population at a given mid interval
Expressed as per 1,000 
Define curse fertility rate. How is it expressed? 
# of live births during a given time interval/ estimated # of women aged 15 44 years
Expressed per 1,000 
Define maternal mortality rate. 
# of deaths in a year from puerperal causes/ # of live births during the same year
**all live births, not all pregnancies 
How is maternal mortality rate expressed? 
per 100,000

Define the crude rate of natural increase in terms of natality rates. 
(# of live births  # of deaths during a given interval) / estimated total population at a given interval

How is crude rate of natural increase expressed? 
per 1,000

Define low birth rate ratio. 
# of live births under 2500 gm during a given interval / # of live births during a given interval

Give the formula for prevalence using incidence of a rare disease and does not have long duration. 
P = Incidence * duration of disease

What is the formula for prevalence using incidence when the disease is not rare OR the disease has a very long duration? 
P = (ID* T) / (ID * T) + 1

Give the formula to estimate risk using the simple cumulative method. 
R = CI = I (t0 , t) / N'0
The # of incident cases between time zero and the end of the study divided by the total number of participants at the beginning of the study (disease free of course) 
What is sensoring in terms of risk estimates? 
The inaccurate portrayal of risk estimates because participants were not followed the entire period or the lack of information conc???

How does one estimate the "effective number" of persons at risk using the actuarial method? 
= (N'o  W/2)
The number of persons beginning the time interval minus half of the # of withdrawls. 
What measure of disease is used to test "etiologic hypotheses"? 
Incidence density

What are the three ways to measure person time? 
1. sum of how much each individual time each person was in study
2. "steady state" pop people come in and out often enough to assume PT = N * dt 3. Don't know indiv. PT as there is no "steady state" so just use midinterval disease free population as the avg. pop. size 
What are the three ways to calculate CI or risk? 
1. simple cumulative
2. actuarial 3. density method 
What assumption is made when using the simple cumulative method? 
that are study participants are followed for the entire study either till the end or until they get disease aka no death to competing causes or withdrawls

What is an assumption made when using the actuarial method to calculate risk? 
Withdrawls occur midinterval of observation time

What a major assumption made when using the density method? 
a closed cohort with no competing risk and the age interval ID remain constant over that ID(not sure what this meanswill ask in OH)

What is the most exact method for calculating risk? 
density method

What are the three assumptions that must be met in order to use CI instead of ID in the density method? 
1. rare disease (< 10%) from rare disease assumption
2. event is inevitable no competing risks (rate is constant w/in each age interval) 3. each agespecific ID is constant over that time period 
Which of the three methods for calculating risk assumes not censoring or withdrawls? 
simple cumulative

What measures of disease can be used for crosssectional studies 
1. point prevalence only existing cases included
2. period prevalence  longer time frame, can include both new and existing cases 
What MOD is best for followup studies/prospective studies? 
Since only new cases are measuredcumulative incidence or incidence density

ratio, rate, or proporiton: 1. CI 2. ID 3. prevalence 4. odds 5. risk ration 6. rate ratio 
1. proportion
2. rate 3. proportion 4. ratio 5. ratio 6.ratio 
What method uses rates to calculate risk? 
Density method

Risk or rate? 1. instaneous potential for change in disease status per unit change in time 2. cumulative incidence 3. probability that an indiv. will develop outcome during a specified time pd., conditional on not dying from something else 4. incidence de 
1. rate
2. risk 3. risk 4. rate 5. rate 6. risk 7. risk 8. rate 9. risk 10. rate 
Can you compare SMR's between studies? 
Nope

Can you compare SRR's between studies? 
Yep.

What are 4 ways to reducing confounding? 
1. stratificatin
2. adjustment 3. propensity scores 4. inverse probability of treatment weighting (IPTW) 
What are some common adjustment techniques? 
1. linear regression
2. logistic regression 3. poisson regression 4. proportional hazard models 
What is simpson's paradox? 
thinks hats if that helps
it is the reversal of cause/effect when the samples are combined 
List three methods in study design to reduce confounding. 
1. Matching.
2. Randomization 3. Restriction 
List two method in study analysis to reduce confounding. 
1. Multivariate analysis
2. Stratify 
List the three criteria for confounder 
1. not on the causal pathway
2. a risk factor for the disease in the unexposed 3. be associated w/ exposure variable 
True/False 1. If it is a confounder then it has to be an effect modifier 2. If it is an effect modifier then it has to be a confounder 
1. False
2. False 
What it the null hypothesis for the test for homogenity? 
The pooled estimator (ORmh) is not different from the stratified estimates.

How do you calculate the degrees of freedom for the test for homogenity? 
N (# of strata)  1

What does rejecting the null hypothesis indicate? 
That there may be effect modification and that it is necessary to report the stratified estimates rather than the overall effect estimator

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