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54 Cards in this Set

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Epidemiology
The study of the development, frequency, distribution, determinants, and consequences of disease in a population
Common Uses of Epidemiological Data
$$$$$ spent by pharmaceutical companies, governments, and NGOs for research
Medical school curricula
Treatment
Prevention
Types of Prevention
Primary prevention (health promotion): Smoking cessation
Secondary prevention (early detection): Screening for colorectal cancer
Tertiary prevention (treatment): Chemotherapy
Types of epidemiological Studies-Descriptive
Population (Correlation)
Example: Countries with lower meat consumption have a lower rate of colon cancer

Individuals:
-Case Reports– often first report if dangerous side effect

-Case Series—detection of pneumocystis carinii pneumonia led to AIDS detection

-Cross-sectional Surveys– Health Interview Study (HIS) periodically done to assess current health of population
Types of Epidemiological Studies --Analytic
Observational

--Cohort studies wither retrospective or prospective

-Prospective is when the investigator follows to observe rates of disease following exposure

e.g., Framingham Heart Study

-Retrospective is when the observer reviews data from the past on the relationship between exposure and disease

e.g.,Shipyard workers death certificates
Types of Epidemiological Studies
Interventional studies (clinical trials)
Count
number of events

e.g.,In 1998, 30708 people in the United States died from firearm-related deaths
Ratio
Numerator and denominator represent counts of different events
e.g.,The 1996 ratio of males to females for melanoma of the skin is 21,800/16,500
Proportion
Numerator is a count of events that satisfy a condition
Denominator is the maximum number of individuals or events that could satisfy the condition in the numerator

e.g.,In 1987 there were 2,123,323 deaths recorded from all causes. Of these 760,353 are attributed to heart disease. What is the proportion of deaths attributed to heart disease
Percentage
a proportion multiplied by 100
Rates
a change in one quantity per unit change in another

e.g., 7 out of 50 individuals develop lung cancer during a 5 year study. The rate of lung cancer development is:
7 / 50 persons*5 years or 7 / 250 person-years
0.028 cases of lung cancer per person-year
Prevalence
Proportion of individuals in a population who have a specified clinical characteristic at a specific point in time
Prevalence=
Cases at a specific time t/Population at time t
use of prevalence
Provides an estimate that an individual will be affected at any point in time
Reflect the status of a condition in a point in time
Allows for comparisons between populations or time periods
Incidence
Number of new cases during a defined period of time
e.g.,Ovarian Cancer Study Reveals a Significant Decline in Incidence Rates A joint study by CDC and the North American Association of Central Cancer Registries found that recent trends between 1992 and 1998 revealed a significant decline in ovarian cancer incidence rates of 1.4% per year for all races combined,
Incidence=
Number of new cases in time period/Population at risk

e.g.,25 workers at an particular automobile factory in Japan developed lung cancer in a 2 year period. 35,000 people are employed by the automobile industry in Japan
-250 workers are in this particular plant
-Answer: 25/250=0.10 incidence over 2 years
Chance
Findings not repeatable
Bias
Systematic errors in collecting or interpreting data resulting in a deviation from the truth.
selection bias:
noncomparable criteria used to enroll participants.
information bias:
noncomparable information is obtained due to interviewer bias or due to recall bias
Detection Bias
Improved detection can give the impression that prevalence has increased
Confounding
a mixing of effects
between the exposure, the disease, and other factors associated with both the exposure and the disease
such that the effects the effects of the two processes are not separated.
Measurements of Association
Allow for comparison between populations
-common are relative risk (RR) and attributable risk (AR), and odds ratio(OR)
case control study
an epidemiologic method that begins by identifying persons with the disease or condition of interest (the cases) and compares their past history of exposure to identified or suspected risk factors with the past history of similar exposures among persons who resemble the cases but do not have the disease or condition of interest (the controls).

e.g.,Of 156 women admitted to the hospital with MI, 23 were current OC users. Of the 3120 control women without MI, 304 were current OC users
Odds Ratio (OR):
estimate the odds that someone with disease has had an exposure. Used in case-control studies
Types of Association with OR
No association=1
Positive association>1
The farther away from 1 the greater the strength of association association
Relative Risk
How much more likely is it that exposed people will get disease than non-exposed people?
Relative Risk
Used in cohort studies
Relative Risk
Incidence Ratio
Relative Risk
=a/(a+b) / c/(c+d)
Relative Risk
incidence of bacteriuria in over the counter
Users over incidence of bacteriuria in non over the counter
Users.
Relative Risk
the percentage of people who got infection that used oral contraceptives over the percentage of people who got the infection that didn’t use oral contraception.
Odds Ratio (OR):
***multiply across collumns****
Odds Ratio (OR):
the percentage of those who used oral contriceptives and had a heart attack over the percentage who didn’t use oral contriception and had a heart attack
Odds Ratio (OR):
= a(d)/b(c)
Risk Difference (RD)
subtractincedence of bacteriuria in non OC users from incedence of bacteriuria in OC users
Mortality rate
number of deaths from a dz/ total population
Morbidity rate
number of cases of non-fatal dz/ total population
Attack rate
number of cases of dz/population at risk
Case-fatality
number of deaths from a dz/of cases of that disease
Case control
odds ratio
Cohort study
relative risk
p value
value that indicates findings could have happened by chance
p-values ______ are unlikely to indicate chance
<0.05
p=0.0009
What are the chances of chance
9 times in 10,000
Analytic
OBSERVATIONAL:
-Case-control
-Cohort
-Retrospective
-Prospective
INTERVENTIONAL:
Clinical trials
Case control studies- Strengths
Good for unusual or rare diseases
Smaller in size, quick, easy, cost-effective
Can use secondary data on disease
More easily replicated
Can test hypotheses
Case control studies - weaknesses
Uncertainty is exposure-disease time relationship
Representativeness of cases or controls
Memory problems
Rare exposure a problem
Survivor problem
Bias potential
Cohort studies
retrospective or prospective studies
starts with people free of disease with varying degree of exposure; from cause to effect
two points in time, individual is unit of observation and analysis
Case Control Trials
Retrospective study design
identifies cases
finds controls
asks about history of exposure
Measure of association
odds ratio****
**OR w/ case control
Sources of cohort subjects
Cohort studies are important when the exposure is known to be noxious and could not be randomly assigned by an investigator as in a clinical trial

Internal comparison

Separate cohort
-As similar as possible to exposed cohort in education, income, gender, race, geographic location

Comparison with available population rates
-Standardized mortality ratio (SMR)
Cohort studies - strengths
determination of incidence and risk
multiple exposures and multiple outcomes
can establish cause - effect
good when exposure is rare
temporal relationship clear
minimizes selection and information bias
Cohort studies - weaknesses
validity affected by losses to follow-up
often requires large sample
ineffective for rare diseases
long time to complete
expensive
subject attrition
confounding by other factors possible