Introduction to Clinical Epidemiology

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Introduction to Clinical Epidemiology

• Spring 1999 Elective
• UT-H HSC
• Jan Risser, PhD and Will Risser, MD PhD

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Epidemiology

• Basic science concerned with the patterns of
  disease frequency in human population
• Distribution of disease by person, place, time
• Assumption
• Disease does not occur randomly
• Disease has identifiable causes
• which can be altered and therefore
• prevent disease from developing

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Definition of Epidemiology

• The study of the distribution and determinants of
  health-related states or events in specified
  population, and the application of this study to
  control of health problems.
• source Last (ed.) Dictionary of Epidemiology,
  1995

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Definition of Epidemiology

• Study surveillance, observation, hypothesis
  testing, analytic research, and experiments.
• Distribution analysis by time, place, and
  person.
• Determinants physical, biological, social,
  cultural, and behavioral factors that influence
  health.
• Health-related states or events diseases,
  causes of death, behavior, reactions to
  preventive regimens, and provision and use of
  health services.

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Definition of Epidemiology

• Specified populations those groups of people
  with identifiable characteristics
• Application to control refers to the goal of
  epidemiology, that is to assess the public health
  importance of diseases, identify the population
  at risk, identify the causes of disease,describe
  the natural history of disease, and evaluate the
  prevention and control of disease

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Aims of epidemiologic research

• Describe the health status of a population
• Explain the etiology of disease
• Predict the disease occurrence
• Control the disease distribution

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Preventable Causes of Disease

• BEINGS
• Biological factors and Behavioral Factors
• Environmental factors
• Immunologic factors
• Nutritional factors
• Genetic factors
• Services, Social factors, and Spiritual factors
• JF Jekel, Epidemiology, Biostatistics, and
  Preventive Medicine, 1996

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Causal model of risk factors for CVD
Morbidity and Mortality (Stroke, MI)
Biological Risk Factors (Hypertension, Blood
Lipids, Homocysteine)
Genetic Risk Factors (Family History)
Behavioral Risk Factors (Cigarette, Diet,
Exercise)
Environmental Factors (Socioeconomic Status, Work
Environment)
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Epidemiology Clinical Medicine

• Epidemiology is used in clinical medicine to
• describe the natural history of diseases
• discuss disease causality
• - proximate biological mechanisms of disease
• - distal social and environmental causes of
  disease
• provide disease surveillance
• - essential for evaluating community health
  problems - - and setting disease control
  priorities
• Greenberg RS (ed.) Medical Epidemiology, 1993

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Epidemiology Clinical Medicine

• Epidemiology is used in clinical medicine to
• evaluate diagnostic testing
• - evaluate usefulness, sensitivity, specificity
• - to set cutoff points, and develop screening
  strategies
• evaluate prognosis
• - by identifying prognostic factors
• - through cohort and case control studies
• Greenberg RS (ed.) Medical Epidemiology, 1993

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Epidemiologic Process

• In the epidemiologic process, researchers
• Define the problem ask a well focused question
• hypothesis statement
• Identify the cause test the hypothesis
• is there an association between exposure and
  outcome
• Interpret the results
• threats to validity (bias, confounding),
• role of chance

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Brief History of EpidemiologyClassical
Infectious Diseases Epidemiology

• Edward Jenner (1749-1823)
• developed a vaccine against smallpox using cow
  pox
• 160 years before virus was identified
• John Snow (1813-1858)
• described the association between dirty water and
  cholera
• 44 years before vibrio was identified
• Ignaz Semmelweis (1818-1865)
• described the association between childbed fever
  and physicians unclean hands
• 32 years before causal agent was discovered

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Brief History of EpidemiologyClassical
Nutritional Epidemiology

• James Lind (1716-1794)
• conducted an experiment which showed that scurvy
  could be treated and prevented with limes,
  lemons, and oranges
• ascorbic acid was discovered 175 years later
• Joseph Goldberger (1874-1927)
• identified that pellagra was not infectious but
  nutritional in origin and could be prevented by
  increasing the amount of animal products in the
  diet and substituting oatmeal for corn grits
• niacin was discovered 10 years later

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Brief History of EpidemiologyEpidemiology of
Chronic Diseases

• Observational Studies
• R Doll AB Hill. Early case-control study.
  Smoking and carcinoma of the lung Preliminary
  report. Br. Med. J. 2739, 1950
• Cohort Studies
• An approach to longitudinal studies in a
  community the Framingham study. 10,000
  residents gave baseline information. Follow-up
  is now 50 years. Annals New York Academy of
  Sciences 1075391963

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Brief History of EpidemiologyEpidemiology of
Chronic Diseases

• Experimental Studies
• Hypertension Detection and Follow-up Program
  Cooperative Group. 10,500 subjects randomly
  assigned to two groups
• 1. stepped care - antihypertensive therapy
  increased stepwise to achieve
• and maintain blood pressure reduction to goal.
• 2. Referred care - subjects were referred to
  their primary care physician and
• treated as usual.
• mortality stepped care 9.0/100 referred care
  9.7/100
• final blood pressure 84.1 in stepped care 89.1
  in referred care

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Brief History of EpidemiologyEpidemiology of
Chronic Diseases

• Physician Health Study
• randomized, placebo-controlled, double-blind
  clinical trial
• conducted entirely through the mail
• 22,071 male physicians enrolled to study the
  effects of aspirin on cardiovascular disease and
  the effects of beta-carotene on cancer
• randomly assigned to one of four groups
• aspirin beta carotene
• active active
• active placebo
• placebo active
• placebo placebo

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Observational and Analytical Epidemiology

• Descriptive epidemiology
• the occurrence of disease (cross-sectional)
• Etiologic epidemiology (quasi-experimental)
• cause of disease (cohort, case-control)
• Experimental epidemiology
• assessment of therapy (cohort, randomized
  clinical trial)

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Research Design Used in Epidemiology

• Case Reports / Case Series
• Case control
• Cohort prospective or retrospective
• Cross sectional
• Qualitative (Randomized Clinical Trials)
• Secondary data analysis

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Definitions in Epidemiology

• Bias
• Confounding
• Frequency Measures
• Prevalence
• Incidence
• Measures of Association
• Causal Inference

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BIAS

• systematic errors in collecting or interpreting
  data such that there is deviation of results or
  inferences 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

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BIAS

• Bias results from systematic flaws in study
  design, data collection, or the analysis or
  interpretation of results.

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Selection BIAS

• Selection bias
• Hospital Mean duration Labor
• deliveries of labor complications
• Season
• Summer 180 8.0 hr 7.8 (14/180)
• Winter 240 10.5 hr 11.7 (28/240)

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Selection BIAS

• DELIVERIES Mean duration Labor
• Hospt. Home All of Labor Complications
• Season
• Summer 180 20 200 8.0 hr 8.0 (16/200)
• Winter 240 160 400 8.0 hr 8.0 (32/400)
• Home deliveries were more common in winter.
  Labor complications among home deliveries were
  low. Women with prolonged or complicated labor
  attempt to reach the hospital no matter what
  season.

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Information BIAS

• Response bias - a systematic error that results
  when subjects respond inaccurately to an
  investigators questions
• Lushton County Medical Society commissioned a
  survey of community perceptions regarding
  physician impairment by alcohol or drugs.
  Biomedical Bestiary. Michael, Boyce Wilcox
• Persons were asked for anonymous impressions
  regarding their personal physician.

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Information BIAS

• 1000 persons were randomly chosen from the
  community and sent a simple postcard
• 1. Is your physicians medical judgment
• ever compromised by the use of alcohol or
  drugs? 0.4
• 2. Does the physician drug or alcohol abuse
  threaten the
• professional image of physicians in
  Lushton? 78
• 3. Are physicians who use drugs or alcohol a
  threat
• to their patients? 85
• 98 response rate

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Information BIAS

• 1000 original respondents re-interviewed after
  12 of the licensed physicians in the county were
  cited for drug- or alcohol-related malpractice.
• 1. Is your physicians medical judgment ever
  compromised by the
• use of alcohol or drugs? 0.4 8
• 2. Does the physician drug or alcohol abuse
  threaten the
• professional image of physicians in
  Lushton? 78 80
• 3. Are physicians who use drugs or alcohol a
  threat
• to their patients? 85 82

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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.

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Confounding

• Confounding results when the effect of an
  exposure on the disease (or outcome) is distorted
  because of the association of exposure with other
  factor(s) that influence the outcome under study.

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Confounding Biomedical Bestiary Michael,
Boyce Wilcox, Little Brown. 1984
Observed association, presumed causation
Gambling
Cancer
Smoking, Alcohol, other Factors
Unobserved association
True association