Lecture 3 - Epidemiology

Question 1

Epidemiology Definition

Answer 1

study of the distribution and determinants of disease frequency among populations

Question 2

History of Epi

Answer 2

Hippocrates, john graunt (differences in male female births and deaths), percival pott scrotal cancer and chimney sweeps, John Snow, cigarettes and lung cancer

Question 3

Use of Epi information

Answer 3

health assessments, aid in clinical decisions, search for causes/risk factors, identify subgroups, evaluate actions/interventions/policies, hazard id,

Question 4

Types of EPI studies

Answer 4

experimental (clinical, community interventions, field trials), non-experimental/observational studies

almost all are observational

Question 5

Types of observation study

Answer 5

descriptive (case series/case studies, proportionate mortality, ecologic studies / correlational studies, cross sectional surveys)
analytic (cross sectional studies, cohort studies (prospective / retrospective), case-control studies)

Question 6

descriptive case-study

Answer 6

single patient or group of patients, lead to more studies

Question 7

descriptive proportional mortality study

Answer 7

based solely on deceased subjects, proportion of exposed dead to unexposed dead. inexpensive and quick and can be reasonable

Question 8

descriptive- ecologic

Answer 8

unit of anlysis is the group (harvard six cities study)

Question 9

descriptive study: cross sectional survey

Answer 9

disease and exposure status of all persons in population, determined at one point in time. used for status and trends. cannot be used to assess causal relationships

his preterm birth study in puerto rico (PROTECT)

Question 10

prevalence vs incidence

Answer 10

incidence: # of new infections per person time (number of exposed cases versus time exposed)
prevalence: # of people currently living with infection

Question 11

analytic study: case-control

Answer 11

cases randomly selected from hypothetical source population,controls are sample of non-diseased comparison subjects, use an odds ratio

[exposed disease / exposed no disease] / [non exposed disease / non exposed no disease]

Question 12

analytic cohort studies

Answer 12

the gold standard. investigator defines groups that have various exposure levels and then watches over time (or analyzes backwards ie retrospective). as close as you can get to causality) IRR and PRR. also RR

Question 13

IRR, PRR, RR

Answer 13

IRR is IRe / IRne
PRR is PRe/PRne

Relative Risk is
[exposed and disease / (total exposed pop)] / [not exposed w/ disease / (total non exposed pop)]

Question 14

Comparison of cohort and case control

Answer 14

case control; simple, low cost, for rare diseases, more susceptible to bias,
cohort; expensive and time-consuming, for relatively common diseases, multiple diseases being explored,provides causal evidence

Question 15

hill criteria for causality

Answer 15

temporality: event occurs after cause
strength: of association
biologic gradient: greater exposure = greater incidence
consistency: across places
plausibility: of mechanism
analogy: to similar factors
experimental evidence:
specificity: shown at a specific site with no other explanation
coherence: epi studies and lab studies

Question 16

Types of Bias

Answer 16

confounding: confusion of the interest by another factor, must be 1) extraneos risk factor for disease 2) associated with exposure in source population 3) cannot be intermediate step in the casual pathway
selection: exposed and non-exposed populations are not truely comparable (volunteerism, healthy worker, attrition)
information: systematic differences in way data are obtained. (recall bias, observation bias) measurement error,

Question 17

Exposure Assessment

Answer 17

measure magnitude, frequency, duration, timing, parameter of interest, exposure vs dose vs biologically effective dose.

Question 18

Hierarchy of exposure assessment approaches

Answer 18

biomarkers, personal measurements, ambient monitoring, surrogate of exposure, distance from site, residence or employment by proximity, residence or employ in area