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INTRODUCTION TO EPIDEMIOLOGY AND BIOSTATISTICS

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Title: INTRODUCTION TO EPIDEMIOLOGY AND BIOSTATISTICS


1
INTRODUCTION TO EPIDEMIOLOGY AND
BIOSTATISTICS Spring 2005
2
INTRODUCTION TO EPIDEMIOLOGY AND
BIOSTATISTICS Spring 2005
Lecture 1 Overview and Causation in
Epidemiologic Investigation Lecturer Hoda
Anton-Culver, PhD Professor and Chief of
Epidemiology Department of Medicine Date
Time April 8th, 100 250pm Topics Ov
erview of Epidemiology and Current
Trends Association versus causation, criteria
for asserting cause Students are responsible
for the book assignment Assignment Read
Jekel Chapters 4, pp 65-70
3
BROAD DEFINITION OF EPIDEMIOLOGY
  • The study of the distribution and determinants of
    health-related states or events in specified
    populations and the application of this study to
    the control of health problems.
  • (Last, JM. Dictionary of Epidemiology)

4
PURPOSE OF EPIDEMIOLOGY
  • To describe the frequency and extent of health
    conditions and disease.
  • To determine the burden of disease in a
    community, including socioeconomic impact of
    disease occurrence in specific populations.
  • To identify the causes and risk factors of
    specific diseases. This is the basis of disease
    prevention.
  • To evaluate medical interventions, including both
    preventive and therapeutic measures, and evaluate
    the delivery of these measures in health care
    settings.
  • To study the natural history and prognosis of
    disease.
  • To provide the foundation for developing public
    policy and regulatory decisions relating to
    health.

5
EPIDEMIOLOGIC DESCRIPTION OF DISEASE
  • Characteristics of persons
  • a. Age
  • b. Sex
  • c. Ethnic groups
  • d. Religion
  • e. Marital status
  • f. Occupation
  • g. Socioeconomic Status
  • Place
  • a. Types of comparisons
  • International
  • Rural Urban
  • Local distributions

6
EPIDEMIOLOGIC DESCRIPTION OF DISEASE
  • Place (cont)
  • b. Characteristics peculiar to place
  • 1. Biologic environment
  • 2. Chemical and physical environment
  • 3. Social environment
  • Time
  • a. Point epidemics
  • b. Secular change
  • c. Cyclic fluctuations
  • d. Clustering in time
  • Combination of person, place and time
  • a. Migrant studies
  • b. Birth cohort studies
  • c. Time place clustering

7
Schematic representation of the natural history
of disease
  • STAGE OF SUSCEPTIBILTY PRE- CLINICAL DIS
    ABILITY
  • DISEASE SYMPTO- DISEASE OR RECOVERY
  • MATIC
  • TISSUE Resolution or
  • CHANGES Pre-Pathogenesis Pathogenesis
    Sequelae
  • LEVEL OF
  • PREVENTION Primary Secondary Tertiary
  • MODES OF Health Promotion Detection Treatment
    and
  • INTERVENTION Specific Early Rehabilitation
  • Protection Diagnosis Limitation of
  • Prompt Disability


Outcome Death
E
Clinical Disease
Chronicity
B
D
C
A
Clinical Horizon
Residual Disability
Inapparent or Subclinical
8
Idealized Conceptualization of the Scientific
Method
Theory/ Knowledge/ Problems
Synthesis Hunches
Inferences Re Conceptual Ho
Conclusions and Interpretations
Conceptual Hypotheses
Inferences Re Operational Ho
Study Design
Operational Hypotheses
Empirical Findings
Data Collection
Observations/ Data
Data Analysis
9
  • Diversity in Approach of Epidemiologic
  • Assessment of the Distribution and Cause of
    Disease in Human Populations
  • Population Research
  • Healthcare aspects Research
  • Prevention Research
  • Basic mechanisms using multiple systems
  • (cell cultures, stem celletc)
  • Genetic/ family-based research
  • Childhood disease research
  • Race/Ethnicity issues
  • Aging and geriatric research
  • Psychosocial/ quality of life research
  • Clinical and Therapeutic trials

10
Health Care Outcome Approachs
Management
Outcome Measures
Patient
Health Care Provider
  • survival
  • recurrence
  • new disease
  • treatment complications
  • health related quality of life
  • disease-specific impairments
  • satisfaction with care
  • financial family burden
  • medical specialty
  • medical coverage/insurance
  • access to clinical trials
  • support group availability
  • prognostic factors
  • knowledge/interest learning about cancer
  • coping strategies
  • quality of life

Treatment/Diagnostic
  • treatment recommendation
  • treatment given
  • appropriateness of treatment
  • pain/symptom management

11
Example of a Pedigree Generated from Expanded
Family History Data File
UC Irvine Epidemiology Division 11/8/2000
Page 11
12
FAMILY HISTORY
Family history is a significant component to
facilitate research studies on a)
Susceptibility to human disease b) Early
detection and prevention c) Genetic testing
including psychosocial/behavioral issues d)
Identification and characterization of
populations at high genetic risk e)
Chemoprevention and other clinical trials f)
Other translational research
13
  • Clinical Research Approaches
  • The risks are highest
  • Professional roles are conflicted
  • Conflict in two directions, to do no harm and
    randomization where 50 of the patients will not
    benefit
  • Clinical research is a multibillion Dollar
    business and has a high potential for profit
    riding on efficiency aggressiveness and positive
    outcome
  • Given the complexity of human research, can
    consent ever be truly informed?

14
Types of Frequency Measures
  • Incidence Measures
  • The numerator reflects the number of new
    (incident) cases of a disease identified during a
    given period.
  • Prevalence Measure
  • The numerator reflects the number of existing
    (prevalent) cases of a disease identified at a
    point in time or during a given period.
  • Mortality Measures
  • The numerator reflects the number of deaths due
    to or with one or more diseases, identified
    during a given period.

15
Incidence Rates
  • Incidence rates are the fundamental measure for
    etiologic studies since they are direct
    indicators of risk of disease over a period of
    time.
  • High incidence rates are synonymous with high
    risk of disease.
  • Measurement of incidence requires at least two
    sets of observations to determine the number of
    new cases of disease that have occurred among the
    initial disease-free individuals during some
    specified period of time.
  • By combining information on incidence rates with
    other variables, we can determine what factors
    may affect the risk of acquiring disease.

16
Prevalence Rates
  • In contrast to incidence rate, prevalence rate is
    a static concept. It provides us with an
    indication of the amount of disease prevailing in
    a given point in time (in a period), thus allows
    assessment of the burden of a particular disease
    in a community.
  • Prevalence depends on
  • Number of people who have become ill in the past
    (previous incidence).
  • The duration of their illness.
  • If 1 and 2 are fairly stable, then
  • Prevalence Incidence x Duration

17
The following characteristics should be
remembered concerning incidence and prevalence
  • Causes and effect, such as smoking and lung
    cancer, if studied simultaneously, it would be
    impossible to establish a time sequence for a
    presumed cause.
  • High prevalence rates may reflect either high
    incidence or long duration.

18
A causal association is one in which a change in
the frequency or quality of an exposure or
characteristic results in a corresponding change
in the frequency of the disease or outcome of
interest.
Causation of Disease
19
Types of Causal Relationships
  • Sufficient cause If the factor (cause) is
    present, the effect (disease) will always occur
    e.g. Genetic disorder such as Tay-Sachs disease.
  • Necessary cause If the factor (cause) is absent,
    the effect (disease) cannot occur e.g.
    Tuberculosis.
  • Risk factor If the factor is present and active,
    the probability that the disease will occur is
    increased e.g. Cigarette Smoking
  • Directly causal association The factor exerts
    its effect in the absence of intermediary factor
    (intervening variable) e.g. Accidents
  • Indirectly causal association The factor exerts
    its effect via intermediary factor e.g. SES.
  • Non-causal association The relationship between
    two variable is statistically significant, but no
    causal relationship exists

20
Guidelines for Disease Causation
21
Common Pitfalls in Causal Research
22
Human Research Approach and Design
Analytic Examine etiology, efficacy
Descriptive To Describe an experience,
programs, treatment, unusual observation
Experimental Evaluate the efficacy of a
therapeutic , or other interventions
Observational Association of cause and
effect Comparison between 2 treatments
Examples 1) Case Reports or series Side
effect of a drug Cluster of cases 2)
Clinical series Cases with West Nile Virus 3)
Population Prevalence or incidence of
disease in populations 4) Ecological study
  • Examples
  • Clinical Trial
  • Community education

Examples 1) Cross-sectional 2) Case-control 3)
Prospective/Cohort
23
Ecological Study Design
  • The strategy is based on determining whether
    those ecological units with a high frequency of
    exposure also tend to be the groups with a high
    frequency of health outcome occurrence.
  • Measure group rates of the health outcome and
    exposure prevalence for the same population
    group, but not necessarily using the same source
    of data.
  • Types of comparisons
  • Geographical or group comparisons, e.g.,
    countries or administrative units.
  • Temporal comparisons
  • Combines geographic and temporal comparisons
  • Time-series studies.

24
Cross-Sectional Study
  • Cross-sectional studies typically conducting a
    medical survey in a community or defines
    population. Key steps in conducting a
    cross-sectional medical survey are
  • To identify the base population
  • To choose a sampling design and sampling frame
    for selecting the study participants
  • To measure exposure and health outcome status on
    the study subjects.
  • A critical aspect of conducting a medical surveys
    is the logistical plans for examining the
    subjects and obtaining and processing any
    biological specimens.
  • Cross-sectional studies may also be based on
    existing records. For example, a study used data
    from NHANES to evaluate the association between
    lead exposure and hypertension by comparing blood
    lead concentrations and blood pressure in the
    survey participants (Schwartz, 1986).

25
Cross-Sectional Study
EC
  • Syn Prevalence study survey
  • A nondirectional or backward design involving
    disease prevalence (C/C) and random sampling from
    a single source population (N), which may be
    stratified. Although cross-sectional studies
    maybe conducted without random sampling, this
    strategy offers little potential for describing a
    larger population or testing etiologic
    hypotheses.
  • Cross-sectional studies are often used to study
    conditions that (1). Are measured on a
    continuous scale and can vary over time (2).
    Are relatively frequent diseases with relatively
    long durations of expression (e.g., nonfatal and
    incurable conditions).

_ EC
_ EC
N
S
__ EC
26
Case Control Study
  • Is a study that starts with the identification of
    persons with the outcome of interest and a
    suitable control group of persons without the
    outcome. The relationship of an exposure to the
    outcome is examined by comparing those with and
    without the outcome with regard to how frequently
    the exposure is present, or if quantitative, the
    levels of exposure in each of the groups
  • Syn Case-referent Study Retrospective Study

27
Case Control Study
  • There are two alternative approaches for sampling
    controls in case-control studies involving
    incident cases
  • Density Sampling one or more controls are
    selected for each case ay the time of case
    detection i.e., matching on time.
  • Cumulative Sampling all controls are selected at
    the end of the observation period during which
    the cases are identified.
  • Density sampling is generally preferable when the
    observation period is long, especially if the
    frequency of exposure changes over time

28
Case-Control Study
  • A backward or nondirectional design in which a
    group of cases- either incident (D, as above) or
    prevalent- are compared to a group of noncases or
    controls ( C ) with respect to previous or
    current exposure status. The ratio of controls-
    to cases is fixed by the investigator. To make
    causal inferences, the investigator must assume
    that the control group ( C ) is representative of
    the same source population (N) from which the
    cases (D) developed.
  • The cases-control study differs from the
    cross-sectional study in two ways In a case
    control study, subject are samples from two
    populations (cases and noncases) and cases may be
    incident or prevalent in a cross-sectional
    study, subjects are sampled from one population
    and cases are prevalent only. (cont.)

DE
_ DE
N
D
_ CE
N
S
_ C
__ CE
29
COHORT STUDIES
  • (also called follow-up studies, longitudinal
    studies, and incidence studies)
  • Cohort study is the method in which subsets of a
    defined population can be identified who are,
    have been, or in the future may be exposed or not
    exposed to a factor or factors hypothesized to
    influence the probability of occurrence of a
    given disease or other outcome.

30
1. Prospective Cohort Studies. When cohort(s)
are assembled in the present and followed into
the future.
  • Specific Exposure Cohorts.
  • When the disease outcomes of a cohort with a
    specific exposure are compared to the same
    disease outcomes of an appropriate unexposed
    cohort. Specific exposure cohorts are preferred
    when the exposure is unique or relatively rare
    (e.g. Hiroshima survivors).
  • General Population Cohorts
  • When the cohort is a sample of the general
    population all of whom are followed for the
    disease outcome. The exposure status of
    individuals members of a general population
    cohort are assessed at the beginning of the study
    (and sometimes periodically throughout the
    study). Cohort studies based on general
    populations are preferred when the exposure of
    interest is relatively common and/or when there
    is interest in investigating more than one
    exposure simultaneously.

31
2. Historical Cohort Studies
  • (also called Retrospective Cohort Studies).
  • When the cohort(s) are assembled from past
    records. Follow-up can be either in the present
    or from more recent past records. Historical
    cohort studies may study either general
    population cohorts or specific exposure cohorts.

32
The Structure of a Cohort Study
DISEASE
EXPOSED
NON-CASES
NO DISEASE
RANDOM SAMPLING
SOURCE POPULATION
DISEASE
NON-EXPOSED
NO DISEASE
PREVALENT CASES
FOLLOW-UP OUTCOME
33
Figure 5-2 Design of cohort study
  • TIME
  • Exposure Disease
  • Study group Present
  • Comparison
  • Group Absent
  • Disease rate for exposed a
  • a b
  • for nonexposed c
  • c d
  • a
  • a b
  • Relative Risk c
  • c d

a
Present
b
Absent
c
Present
Absent
d
34
Sampling strategies for Epidemiologic Studies
Population
Exposed
Random Sample
Controls
Cases
Unexposed
35
STRATEGY FOR REVENTION
  • (1) RISK ASSESSMENT
  • A) EXPOSURE.
  • MONITOR POTENTIAL CARCINOGENS IN AIR, IN
    WATER, SOIL AND THE HOME.
  • USE DATA FROM REGISTRIES OF ENVIRONMENTAL
    ACCIDENTS.
  • B) POPULATIONS AT HIGH RISK FOR CANCER.
  • IDENTIFY AND MONITOR FOR INCIDENCE AND
    PREVALENCE

36
STRATEGY FOR REVENTION
  • (2) INTERVENTION
  • A) EDUCATION AND HEALTH PROMOTION
  • B) CONTROL EXPOSURE TO KNOWN CARCINOGENS
  • C) POPULATION TRIALS
  • IMMUNIZATION, CHEMO-PREVENTION AND
  • BIOLOGICAL MARKERS FOR EARLY DETECTION
  • D) GENETIC TESTING AND PSYCHOSOCIAL SUPPORT
  • E) EARLY DETECTION

37
STRATEGY FOR PREVENTION
  • (3) EVALUATION
  • A) MEASURE CHANGE IN RISK
  • USING CPRR's MONITORING OF INCIDENCE,
    STAGE AT DIAGNOSIS, USE OF HEALTHIER LIFESTYLE
    PREVENTION PRACTICES.
  • (4) MODIFY INTERVENTION STRATEGIES
  • A) BASED ON EVALUATION RESULTS
  • B) BASED ON NEW SCIENTIFIC FINDINGS

38
Strategy for Prevention
Identify
A
Populations
s
s
at High
Modify Existing
e
Disease Risk
s
Intervention
s
(based on demography / family history,
host factors..)
m
Programs

e
n
n
o
t

i

t


n

Assess

e

Evaluate

v
Exposure


r


Intervention
e



t
Programs
n
I
Conduct
Research on

Mechanisms
Apply
(including the study of genetic susceptibility)

Population-Based
Intervention
Programs
Epidemiology Division
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