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LECTURE # 10 – EPIDEMIOLOGY & STUDY DESIGNS
What is the DEFINTION of EPIDEMIOLOGY?
o The study of the distribution and determinants of health-related states in
specified populations and the application of this study to control health
What is the DEFINITION of DEMOGRAPHY?
o The scientific study of human populations, including their size, composition,
distribution, density, and growth as well as the causes and socio-economic
consequences of changes in these factors.
What the different TYPES of EPIDEMIOLOGY?
o CLINICAL - internally within the body
o SOCIAL - behaviourally
o CRITICAL – structurally, contextually
o COMMUNITY - happens in community
o OCCUPATIONAL – happens in the workplace
What are the TWO classes of EPIDEMIOLOGICAL STUDIES?
o EXPERIMENTAL – exposure is varied to detrmien how many get the
o OBSERVATIONAL – occurrence of disease is observed in people who are
What are the TWO main types of STUDY DESIGNS?
o DESCRIPTIVE – disease and related factors are measure, used when
health problem is suspected and you want to develop hypotheses
What are the TYPES of DESCRIPTIVE STUDY DESIGNS? Describe them!
o CORRELATIONAL STUDIES: Correlational studies, data from entire
population is used, cannot link exposure to diease in the same person
o CASE REPORTS: profile of a single person
o CASE SERIES: describes the characteristics of a number of patients
o CROSS SECTIONAL STUDY – exposure and disease measured at one one
point in time, survey population of interest, temporal association
cannot be clearly determined
What are the TYPES of ANALYTICAL STUDY DESIGNS?
o PROSPECTIVE COHORT – idnividuals are grouped based on exposure
status and follow up to determine if exposure increases, decreases or
has no effect on the development of disease
We do it when there is STRONG suggestion of ASSOCIATION,
exposure is RARE, and there is a SHORT average time between
EXPOSURE and DISEASE
Advantages: Expensive, Time Consuming, Loss to Follow Up,
Limited to Rare Opportunities, Ascertainment of Disease
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Advantages: Classification before the disease develops,
Calculation of incidence rates among exposed and not exposed,
Calculate risk directly, Observation of Many Outcomes, Efficient
for Rare Exposures
o HISTORICAL/RETROSPECTIVE COHORT
Cases based on exposure status, Retrspective examination,
Time of Disease Development Cannot be Ascertained, Study
Design Requires Less Time
o CASE CONTROL – Selected on basis of disease
Cases – Disease
Controls – No Disease
Features: Cases and controls should be similar, Data
(Interviews, Employment Records, and Medical Records to
determine possible exposures)
Benefits: Rare disease, Mutliple exposures can be measured,
o RANDOMIZED CONTROL TRIALS (RCT)
Researcher randomly assigns patients to one treatment and
other patients to a placebo, or usual treatment.
Features of RCT: Classic way to evaluate effectiveness of diverse
treatments, follow up prospectively
What are MIXED Study Designs?
o Can use both descriptive and analytical
Which type of study has KNOWN EXPOSURE?
o Cohort Study
Which type of study has KNOWN OUTCOME?
What is RELATIVE RISK?
o The differential risks for different exposures
What is RELATIVE RATE RATIO?
What is RELATIVE ODDS RATIO?
How do you calculate RELATIVE RISK RATIOS?
o Incidence proportion in exposed population / Incidence proportion in
unexposed proportion = RR
What does it mean if your RELATIVE RISK RATIO is EQUAL to 1?
o No difference in incidence
What does it mean if your RELATIVE RISK RATIO is GREATER THAN to 1?
o Incidence is more in the exposed group
What does it mean if your RELATIVE RISK RATIO is LESS THAN to 1?
o Incdience is less in the exposed group
What is the PURPOSE of STANDARDIZATION OF MORTALITY RATES?
o To help control for the effects of age or other variables because for example,
young people die less often than older people. We need something to help
account and fix for that.
What are the TWO methods of STANDARDAZATION? Ajustment and
standardization refer to the procedures for facilaiting the comparison of
summary measures across group
o Remove effects of extraneous factors
o What is DIRECT STANDARDIZATION?
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A proportion in each age group of a standard population are
applied to the age-specfic death rates of the population being
o What is INDIRECT STANDARDIZATION?
A standard population is used to provide age specific death rates.