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Evidence Based Chronic Disease Prevention Module Three : Quantifying the Issue. Presented by: Karen Peters, DrPH. Objectives. Understand the basic concepts of descriptive epidemiology Understand the major designs and contributions of analytic epidemiology

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Evidence Based Chronic Disease Prevention Module Three : Quantifying the Issue


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evidence based chronic disease prevention module three quantifying the issue

Evidence Based ChronicDisease PreventionModule Three:Quantifying the Issue

Presented by: Karen Peters, DrPH

objectives
Objectives
  • Understand the basic concepts of descriptive epidemiology
  • Understand the major designs and contributions of analytic epidemiology
  • Be more knowledgeable of several major sources of public health surveillance data.

Evidence Based Chronic Disease Prevention

epidemiology
Epidemiology
  • The basic science and fundamental practice of public health and preventive medicine
  • Epidemiology comes from epidemic - in Greek ‘upon the people’
    • Hippocrates, Airs, Waters, Places…Consider the context in which people live, the airs ‘peculiar to each particular region’, the ‘properties of the waters’, and ‘the mode of life of the inhabitants, whether they are heavy drinkers, taking lunch, and inactive, or athletic, industrious, eating wisely and drinking little.’

Evidence Based Chronic Disease Prevention

uses of epidemiology
Uses of Epidemiology
  • Historical study: Is community health getting better/worse?
  • Community assessment: What actual and potential health problems are there?
  • Working of health services (Efficacy, Effectiveness, Efficiency)
  • Individual risk and chances (Actuarial risks, Health hazard appraisal)
  • Completing the clinical picture: Different presentations of a disease
  • Identification of syndromes
  • Search for causes: case control and cohort studies
  • Evaluation of presenting symptoms and signs
  • Clinical decision analysis

Evidence Based Chronic Disease Prevention

epidemiologic reasoning
Epidemiologic Reasoning
  • Disease is not randomly distributed in a population.
  • Measurable factors influence the pattern of disease and the underlying causes of disease
  • Disease causation is multi-factorial.
    • Multiple factors interact to create an environment in which disease occurs.

Evidence Based Chronic Disease Prevention

epidemiologic reasoning6
Epidemiologic Reasoning
  • Epidemiology is the study of the distribution and determinants of health-related states and events in specified populations and the application of this study to the control of health problems.

Evidence Based Chronic Disease Prevention

epidemiologic reasoning7
Epidemiologic Reasoning:
  • Distribution
    • Patterns of disease within or across defined populations
    • Relates to time, place and person
    • Descriptive epidemiology

Evidence Based Chronic Disease Prevention

epidemiologic reasoning8
Epidemiologic Reasoning:
  • Determinants
    • Factors that influence the prevention, occurrence, control, and outcome of disease
    • 2 types of determinants: host and environmental
      • Host: determine susceptibility of individual (e.g. age, sex, genetics, race, physiologic state, nutrition state)
      • Environmental: determine hosts exposure to specific agents (e.g. conditions of living, family size, composition, crowding, geography, climate)
    • Analytic epidemiology

Evidence Based Chronic Disease Prevention

general considerations
General Considerations
  • Major public health planning data use rates/ratios that must be evaluated when making health planning and policy decisions
  • Rates/ratios provide basis for most public health assessment and are integral to analyzing process and outcome measures

Evidence Based Chronic Disease Prevention

measures of disease frequency
Measures of Disease Frequency
  • Two Types of Frequency Measures
    • Attribute Data
      • Counts
    • Variable Data
      • Proportions
      • Ratios
      • Rates

Evidence Based Chronic Disease Prevention

measures of disease frequency11
Measures of Disease Frequency
  • Count = number of events

» 15.7 million diabetic cases (nationally – ADA)

    • Attribute data

Evidence Based Chronic Disease Prevention

measures of disease frequency proportion
Measures of Disease Frequency: Proportion
  • A proportion is the expression of one part to the whole
  • Proportion (part to whole): a/a+b
  • Numerator: People with the disease, condition or event
  • Denominator: All people (with and without the disease, condition or event)
  • Numerator is always included in the denominator - females/females + males

Evidence Based Chronic Disease Prevention

measures of disease frequency proportion13
Measures of Disease Frequency: Proportion
  • Proportion = number of events divided by the population from which the events occurred

» 15,700,000 diabetic cases

266,100,000 population

= 0.059 diabetic cases* (5.9%)

    • variable data * Percentage is a proportion multiplied by 100 percent

Evidence Based Chronic Disease Prevention

measures of disease frequency ratio
Measures of Disease Frequency: Ratio
  • A ratio is always defined as a part divided by another part
  • Ratio (part to part): a/b
  • Numerator: People with the disease, condition or event
  • Denominator: People without the disease, condition or event
  • Numerator is not included in the denominator - females/males

Evidence Based Chronic Disease Prevention

measures of disease frequency ratio15
Measures of Disease Frequency: Ratio
  • Ratio = number of events divided by another number

» 15.7 million individuals with diabetes

250.4 million individual without diabetes

    • variable data

Evidence Based Chronic Disease Prevention

measures of disease frequency rate
Measures of Disease Frequency: Rate
  • A rate measures the occurrence of an event in a population over time
  • Rate (part to whole over time): (a/a + b) x k
  • Numerator: People with the disease, condition or event in a given period
  • Denominator: All people (with and without the disease, condition or event)
  • Numerator: Number of individuals something happened to in the population-at- risk- deaths/population x 10,000 = deaths per 10,000

Evidence Based Chronic Disease Prevention

measures of disease frequency rate17
Measures of Disease Frequency: Rate
  • Remember:
    • Cases in the numerator must come from the population-at-risk
    • The denominator must be the population-at-risk for the event (should have been able to experience the event)
    • Numerator and denominator should cover the same time period
    • All rates are multiplied by an appropriate constant (i.e., 100; 1,000; 100,000)

Evidence Based Chronic Disease Prevention

measures of disease frequency rate18
Measures of Disease Frequency: Rate
  • Rate = number of events divided by the population from which the events occurred, during a defined period

» 15,700,000 diabetic cases in one year

266,100,000 population

= 0.059 diabetic cases per year

    • variable data

Evidence Based Chronic Disease Prevention

measures of disease frequency rate19
Measures of Disease Frequency:Rate
  • Rates are usually expressed as a whole number for a given population during a specified period.

0.059 diabetic cases per year x 100,000

= 5,900 diabetic cases / 100,000 individuals / year

Evidence Based Chronic Disease Prevention

measures of disease frequency rate20
Measures of Disease Frequency: Rate
  • Questions to ask about a rate:
    • What kind of rate is it? (crude, stratified, adjusted)
    • What is it a rate of? (mortality, morbidity, fertility)
    • To what population or group does the rate refer? (US, IL, county, children, adults, older adults)
    • How was the information obtained? (vital records, census, hospital discharge, BRFSS, face to face, telephone, paper/pencil)

Evidence Based Chronic Disease Prevention

guidelines for using rates
Guidelines for Using Rates
  • Ecological fallacy - generalizing data collected in a particular area, to all the individuals living in that area
    • derive indicators from a denominator that includes the entire population group
    • apply indicators with subgroup denominators only to the persons in that subgroup
  • Variations in Base - rates should be accompanied by an indication of its base to be meaningful
    • Ask, “rate per what?”

Evidence Based Chronic Disease Prevention

guidelines for using rates22
Guidelines for Using Rates
  • False Association - Forgetting that rates apply to aggregates not individuals
    • don’t assume each individual possesses the characteristics shown to be associated at the neighborhood level
  • Small denominators and variance of rates - As population base decreases, statistical variation becomes more prominent as an explanation for observed differences
    • Calculate confidence limits

Evidence Based Chronic Disease Prevention

proportions ratios and rates again
Proportions, Ratios and Rates Again!
  • Not 3 distinctly different kinds of frequency measures
    • All are ratios
    • Proportions are a particular type of ratio
    • Some rates are a particular type of proportion
  • Numbers are converted into proportions, ratios and rates to generate comparable indices
    • EX: #/deaths for 2 groups at 2 different times, # differs due to size of population at risk - converting to rate (deaths/10,000) effect size is removed and rates can be compared

Evidence Based Chronic Disease Prevention

measures of disease frequency rates
Measures of Disease Frequency: Rates
  • Question: Do rates distinguish between existing and new cases of diabetes?

Evidence Based Chronic Disease Prevention

measures of disease frequency prevalence vs incidence
Measures of Disease Frequency: Prevalence vs. Incidence
  • Prevalence is the number of existing cases of diseases in a population during a defined period. [15.7 million people (5.9%) have diabetes]
  • Incidence is the number of new cases of disease that develop in a population at risk during a defined period. [798,000 new cases diagnosed per year]

Evidence Based Chronic Disease Prevention

measures of disease frequency prevalence vs incidence26
Measures of Disease Frequency: Prevalence vs.. Incidence
  • Example: National prevalence rate of diabetes

=15.7 million diabetic cases/year

266.1 million individuals

= 0.059 diabetic cases per year (5.9%)

  • Example: National incidence rate of diabetes

= 798, 000 new diabetic cases in 1 year

266, 100, 000 individuals

= 0.0030 diabetic cases per year x 100,000

= 300 new diabetes cases/100,000/year

Evidence Based Chronic Disease Prevention

measures of disease frequency prevalence
Measures of Disease Frequency: Prevalence
  • Includes newly diagnosed (new) and prior surviving (or existing) cases of disease in a population during a defined period.
  • Sometimes called point prevalence, period prevalence, or “prevalence rate.”

Evidence Based Chronic Disease Prevention

measures of disease frequency point prevalence
Measures of Disease Frequency: Point Prevalence
  • Point Prevalence: attempts to measure disease a one point in time
    • When term ‘prevalence’ is used usually refers to ‘point prevalence’
    • # existing cases of a disease at a point in time Estimated total population at same point in time

Evidence Based Chronic Disease Prevention

measures of disease frequency period prevalence
Measures of Disease Frequency: Period Prevalence
  • Period Prevalence: compound measure, constructed from prevalence at a point in time, plus new cases (incidence) and recurrences during the time period (over one year)
    • # of existing cases of a disease during interval Estimated population at mid- interval (Average population)

Evidence Based Chronic Disease Prevention

measures of disease frequency prevalence30
Measures of Disease Frequency: Prevalence
  • Prevalence is a function of both incidence and duration of the disease.
  • P = I x D (when I and D are fairly stable)
    • Rare diseases, (e.g., diabetes), can have relatively high prevalence, if disease duration is long.
    • Common diseases, (e.g., head lice), can have moderate or low prevalence, if duration is short.

Evidence Based Chronic Disease Prevention

characteristics of prevalence
Characteristics of Prevalence
  • Cause and effect measured simultaneously
    • Impossible to infer causation
  • Useful for planning (e.g. beds, clinics, workforce needs)
  • High prevalence  high risk
    • could reflect increased survival(improved care, behavior change - long duration)
  • Low prevalence  could reflect rapid fatal or cure process - short duration)
  • Easy to obtain need only 1 measurement

Evidence Based Chronic Disease Prevention

measures of disease frequency prevalence32
Measures of Disease Frequency: Prevalence
  • Question: How is the prevalence affected?
    • A substantial improvement in treatment for those with diabetes (example: pancreatic  islet cell transplant)
    • A large influx of immigrants with higher rates of diabetes.

Evidence Based Chronic Disease Prevention

measures of disease frequency incidence
Measures of Disease Frequency: Incidence
  • 2 major measures of incidence
    • Cumulative incidence
    • Incidence density

Evidence Based Chronic Disease Prevention

measures of disease frequency cumulative incidence
Measures of Disease Frequency: Cumulative Incidence
  • Measures the proportion of individuals in the population who develop the disease within a defined period.
    • This is a measure of risk, or the probability that an individual in the population will develop the disease over a specified period, assuming that the individual does not die from any other disease during the same period.
    • # new cases dx reported during a time interval Population at risk at start of time interval

Evidence Based Chronic Disease Prevention

cumulative incidence
Cumulative Incidence
  • Cumulative = number of new cases of disease incidence in the total population at risk
  • = 798, 000 new diabetic cases during one year

266, 100, 000 individuals

= 0.0030

= 300 diabetes cases/100,000 individuals / year

  • Question: Can we follow all individuals in the population for one year to determine whether or not they develop diabetes?

Evidence Based Chronic Disease Prevention

incidence density
Incidence Density
  • Measures the rate at which new cases of disease occur in the population at risk during a defined period
  • The population at risk is dynamic and each person in the population contributes the amount of time that they remained under observation and free from disease (person-time)

Evidence Based Chronic Disease Prevention

incidence density37
Incidence Density
  • For incidence density, the denominator is measured in person-time units rather than persons, which accounts for…
    • Persons who enter the population after the study period begins,
    • Persons who are ‘lost’ during the study period, and
    • Persons who develop the disease during the study period and are no longer at risk of developing the disease

Evidence Based Chronic Disease Prevention

incidence density38
Incidence Density
  • Total person-time for the denominator is computed by either…
    • Summing the amount of person-time contributed by each person in the population during the study period, or
    • Multiplying the average size of the population at the mid-point of the study period times the number of years representing the total study period

Evidence Based Chronic Disease Prevention

incidence density39
Incidence Density
  • Incidence Density
    • = number of new cases of disease in one year Total person-years
    • = 798, 000 new diabetic cases during one year

266, 100, 000 person-years

= 0.0030

= 300 diabetes cases/100,000 person-years

Evidence Based Chronic Disease Prevention

characteristics of incidence
Characteristics of Incidence
  • Direct indicator of risk
    • high incidence = high risk of disease
    • Low incidence usually means low risk of disease
  • Incidence rates often underestimated
    • Incomplete reporting
    • Subject to seasonal variation

Evidence Based Chronic Disease Prevention

exercise calculation of person time for incidence density
Exercise: Calculation of person-time for incidence density
  • Go To Handout #1: Module 4
  • Figure out # of years each person represents
  • Figure out # of cases during study period
  • Incidence density = # cases/person-time x 100

Evidence Based Chronic Disease Prevention

solution for incidence density calculation
Solution for Incidence Density Calculation
  • Person A: 5.0
  • Person B: 3.0
  • Person C: 2.0
  • Person D: 4.0
  • Person E: 1.5
  • Total: 15.5 person years
  • Incidence = 2 cases/15.5 person-years x 100
  • = 12.9/100 person-years of observation

Evidence Based Chronic Disease Prevention

incidence and prevalence compared and contrasted
Incidence

# new cases of dx during a specific period of time

measure # of new cases of dx in pop during specific time period

dynamic concept/ measures risk

Prevalence

# existing cases of DX during particular point in time

measure # of individuals with dx in pop at a given point in time

static concept/ measures burden

Incidence and Prevalence: Compared and Contrasted

Evidence Based Chronic Disease Prevention

measures of disease frequency44
Measures of Disease Frequency
  • Question: Is it prevalence (what type) or incidence?
  • Do you currently have asthma?
  • Have you had asthma during the last 5 years?
  • Have you ever had asthma?

Evidence Based Chronic Disease Prevention

measures of disease frequency primary secondary attack rates
Measures of Disease Frequency:Primary/Secondary Attack Rates
  • Primary Attack Rate:
    • # new cases of dx reported during an epidemic Population at start of epidemic period
  • Secondary Attack Rate:
    • # new cases dx among contacts of known cases Size of contact population at risk

Evidence Based Chronic Disease Prevention

interpretation of rates
Rate Type

Crude

Category-specific

Standardized

Rate Meaning

Un-adjusted

Stratified

Adjusted

Interpretation of Rates

Evidence Based Chronic Disease Prevention

measures of disease frequency crude or unadjusted rates
Measures of Disease Frequency: Crude (or unadjusted) rates
  • Estimate the actual disease frequency for a population
  • Can be used to provide data for allocation of health resources and public health planning
  • Can be misleading if compared over time or across populations.
    • For example, the number of persons nationally with diagnosed diabetes increased from 1.6 million in 1958 to 8 million in 1995 a fivefold increase.

Evidence Based Chronic Disease Prevention

measures of disease frequency crude or unadjusted rates48
Measures of Disease Frequency: Crude (or unadjusted) rates
  • For example, the number of persons nationally with diagnosed diabetes increased from 1.6 million in 1958 to 8 million in 1995 a fivefold increase.

Evidence Based Chronic Disease Prevention

measures of disease frequency category specific or stratified rates
Measures of Disease Frequency: Category-specific (or stratified) rates
  • Category specific (stratified rates)
  • are “crude rates” for subgroups of the total population. For diabetes:
    • 6.3 million (18.4%) of all people age 65 or older
    • 11.3 million (7.8%) of all non-Hispanic whites
    • 2.3 million (10.8%) of all non-Hispanic blacks
    • 1.2 million (10.6%) of all non-Hispanic Mexican Americans
    • 8.1 million (8.2%) of all women have diabetes

Evidence Based Chronic Disease Prevention

measures of disease frequency category specific or stratified rates50
Measures of Disease Frequency: Category-specific (or stratified) rates
  • Provide more detailed information than crude rates about patterns of disease frequency in different populations
  • Can be used for valid comparison of populations
  • Can be cumbersome if there is a large number of categories to compare.

Evidence Based Chronic Disease Prevention

measures of disease frequency category specific or stratified rates51
Measures of Disease Frequency: Category-specific (or stratified) rates
  • Category-specific rates can provide general characteristics of the frequency of disease in a population, particularly by …
    • Person
    • Place
    • Time

Evidence Based Chronic Disease Prevention

measures of disease frequency category specific or stratified rates52
Measures of Disease Frequency: Category-specific (or stratified) rates
  • Person:
    • Who has the lowest / highest disease rates in the population?
    • Age Gender
    • Race / Ethnicity  Socioeconomic class
    • Martial Status  Occupation
    • In case of diabetes, a special category specific rate would be if it is gestational related.

Evidence Based Chronic Disease Prevention

measures of disease frequency category specific or stratified rates53
Measures of Disease Frequency: Category-specific (or stratified) rates
  • Place:
    • Where are the lowest / highest disease rates for a population?
    • geographic location
    • population density
    • urban / rural
    • migration
    • environmental factor
    • Exposure to specific agents

Evidence Based Chronic Disease Prevention

measures of disease frequency category specific or stratified rates54
Measures of Disease Frequency: Category-specific (or stratified) rates
  • Time:
    • Are the disease rates changing over time for a population?
    • short-term trends
    • long-term or secular trends
    • cyclic trends
    • clusters
    • intervals from exposure to disease onset
    • age, period, and birth cohort effects

Evidence Based Chronic Disease Prevention

measures of disease frequency standardized or adjusted rates
Measures of Disease Frequency: Standardized (or adjusted) rates
  • Are adjusted for differences in population characteristics, (e.g., Age, race, gender, to allow for unbiased comparisons of disease frequency over time or across populations).
  • Are hypothetical, since they do not represent the actual disease frequency of the populations that are being compared to the reference population.

Evidence Based Chronic Disease Prevention

measures of disease frequency standardized or adjusted rates56
Measures of Disease Frequency: Standardized (or adjusted) rates
  • Example: Compare death rates between 2 populations, must account for age composition
    • Older adults have higher # of deaths per 1,000
    • If population is heavily weighted by older people, comparison between the 2 groups may reflect age discrepancy rather than true differences in mortality experience
    • MUST MAKE ADJUSTMENTS - How?

Evidence Based Chronic Disease Prevention

measures of disease frequency standardized or adjusted rates57
Measures of Disease Frequency: Standardized (or adjusted) rates
  • Two ways to account for differences (age) when comparing crude rates between populations:
    • Compare category-specific rates among the populations that are being compared, OR
    • Adjust (or standardize) crude rates for the populations that are being compared.
      • rates are adjusted to what would be if the two populations being compared had the same age distributions as some arbitrarily selected standard population
        • Direct Adjustment (see notebook)
        • Standardized Mortality Ratio (SMR) (see notebook)

Evidence Based Chronic Disease Prevention

crude and age adjusted rates compared
Year Crude Age-Adjusted

Mortality Rate (to 1940 pop) Rate/1,000

1940 10.8 10.8

1960 9.5 7.6

1980 8.8 5.9

1983 8.6 5.5

1987 8.7 5.4

Table shows crude and age-adjusted mortality rates for US at 5 time periods

Adjustment is made to the age distribution of the population in 1940 (standard)

In 1987 the age-adjusted rate was 5.4/1,000 people

In 1987 the crude mortality rate was 8.7/1,000

Crude and Age-Adjusted Rates Compared

Evidence Based Chronic Disease Prevention

crude and age adjusted rates compared59
Year Crude Age-Adjusted

Mortality Rate (to 1940 pop) Rate/1,000

1940 10.8 10.8

1960 9.5 7.6

1980 8.8 5.9

1983 8.6 5.5

1987 8.7 5.4

If 1987 age distribution was the same as in 1940, the death rate would have been only 5.4/1,000

The crude and adjusted rates for 1940 are the same because it is the standard population

Age-adjusted rates tell you how many would have died if age compositions were the same in the 2 groups

Crude and Age-Adjusted Rates Compared

Evidence Based Chronic Disease Prevention

advantages and disadvantages of using crude rates for community health assessment
Advantages

Easy to calculate.

Summary rates.

Widely used for international comparisons (despite limitations)

Disadvantages

Because population groups vary by demographics etc., the difference in crude rates is not directly interpretable

Advantages and Disadvantages of Using Crude Rates for Community Health Assessment

Evidence Based Chronic Disease Prevention

advantages and disadvantages of using specific rates for community health assessment
Advantages

Applied to homogeneous subgroups.

The detailed rates are useful for epidemiologic and public health purposes

Disadvantages

Comparisons can be cumbersome if many subgroups are calculated for two or more populations

Advantages and Disadvantages of Using Specific Rates for Community Health Assessment

Evidence Based Chronic Disease Prevention

advantages and disadvantages of using adjusted rates for community health assessment
Advantages

Represents a summary rate.

Differences in composition of groups reviewed allowing unbiased comparison

Disadvantages

Not true rates (fictional).

Magnitude of rates is dependent on the standard million population chosen.

Trends in subgroups can be masked

Advantages and Disadvantages of Using Adjusted Rates for Community Health Assessment

Evidence Based Chronic Disease Prevention

community health diagnosis using crude and adjusted rates
Relative Status of Crude Adjusted

Rate Rate

Low Low

Low High

High Low

High High

Community Diagnosis

Low mortality is not due to age, race, sex factors; other mortality conditions are favorable

Low mortality is due to favorable age, race, sex factors; other mortality conditions are unfavorable

High mortality is due to unfavorable age, race, sex factors; other mortality conditions are favorable

High mortality is not due to age, race, sex factors; other mortality conditions are unfavorable

Community Health Diagnosis Using Crude and Adjusted Rates

Evidence Based Chronic Disease Prevention

measures of disease frequency summary
Measures of Disease Frequency: Summary
  • Three important uses for measures of disease frequency:
    • describe - to quantify the burden of disease, disability or death within a defined population
    • compare - to provide the basis for comparison of disease frequency among differing populations
    • predict - to estimate the likelihood (or risk) of developing disease for an average individual within a defined population

Evidence Based Chronic Disease Prevention

descriptive epidemiology
Descriptive Epidemiology
  • Evaluating variations in the frequency of disease allows us to…
    • Identify high risk populations
    • Prioritize public health resources
    • Generate hypotheses about disease causation

Evidence Based Chronic Disease Prevention

analytic epidemiology
Analytic Epidemiology
  • Determinants: Factors that influence the prevention, occurrence, control and outcome of disease
  • Identifying these factors and quantifying their contribution to disease burden are the tasks of analytic epidemiology

Evidence Based Chronic Disease Prevention

analytic epidemiology study designs
Observational

ecological

cross-sectional

case-control

cohort

Experimental

randomized clinical (field) trials

group randomized trials

Analytic Epidemiology: Study Designs

Evidence Based Chronic Disease Prevention

analytic epidemiology68
Analytic Epidemiology
  • Study designs
    • descriptive studies are generally designed to evaluate the magnitude of disease, not test specific causal hypotheses
    • analytic studies are designed to evaluate a priori hypotheses

Evidence Based Chronic Disease Prevention

analytic epidemiology69
Analytic Epidemiology
  • Ecological (or correlational) studies
    • based on aggregated data within or across populations rather than individual level information
    • good for generating ideas, but cannot be used to assess causal relationships

Evidence Based Chronic Disease Prevention

analytic epidemiology70
Analytic Epidemiology
  • Cross-sectional (or prevalence) studies
    • individual-level data derived from cross-sectional surveys
    • temporal sequence from exposure to disease onset usually cannot be established
    • good for generating ideas, but cannot be used to assess causal relationships

Evidence Based Chronic Disease Prevention

analytic epidemiology71
Analytic Epidemiology
  • Case-control studies
    • study participants are grouped by current disease status
    • exposures prior to disease onset are ascertained for study participants
    • temporal sequence from exposure to disease onset can be determined

Evidence Based Chronic Disease Prevention

analytic epidemiology72
Analytic Epidemiology
  • Cohort studies
    • study participants are grouped by prior exposure status
    • study subjects are followed over time to measure frequency of disease
    • temporal sequence from exposure to disease onset can be determined

Evidence Based Chronic Disease Prevention

analytic epidemiology73
Analytic Epidemiology
  • Randomized trials
    • study participants are randomized to specific exposure (or treatment) groups
    • study subjects are followed over time to measure frequency of disease
    • ‘gold standard’ for showing causal associations

Evidence Based Chronic Disease Prevention

analytic epidemiology74
Analytic Epidemiology
  • Hierarchy of Research Design Quality
    • Randomized, prospective, community and/or clinical trial (Cochrane and Campbell collaborations)
    • Cohort studies
    • Case-control studies
    • Cross-sectional studies (prevalence studies)
    • Descriptive/ecologic (correlational) studies
    • Case series/case reports
    • Individual evidence (personal experience/expert opinion)

Evidence Based Chronic Disease Prevention

analytic epidemiology75
Analytic Epidemiology
  • Measures of association
    • relative risk
      • measures the risk of disease in the exposed population relative to the risk in the unexposed population
      • measures the strength of the exposure-disease association
      • RR = 0% (no attributable risk)

Evidence Based Chronic Disease Prevention

analytic epidemiology76
Analytic Epidemiology
  • Measures of association
    • risk difference
      • measures the difference in disease rates between the exposed and unexposed populations
      • RD = 0 (no difference)

Evidence Based Chronic Disease Prevention

analytic epidemiology77
Analytic Epidemiology
  • Measures of association
    • population attributable risk
      • measures the proportion of disease in the population that is attributed to the exposure
      • PAR = 0% (no attributable risk)

Evidence Based Chronic Disease Prevention

analytic epidemiology78
Analytic Epidemiology
  • Types of Bias
    • Selection bias
    • Information bias
    • Confounding bias

Evidence Based Chronic Disease Prevention

causal inference
Causal Inference
  • strength of exposure-disease association
  • dose-response relationship
  • temporal sequence
  • biological plausibility
  • consistency of findings with other studies
    • quality of study design, data and analysis

Evidence Based Chronic Disease Prevention

causal inference80
Causal Inference
  • goal is to provide epidemiologic evidence that helps support or refute a hypothesis
  • this evidence is considered in the context of other evidence to make an informed judgement as to the causal nature of the relation, and whether action is justified

Evidence Based Chronic Disease Prevention

epidemiological sequence
Epidemiological Sequence
  • Observing
  • Counting cases or events
  • Relating cases or events to the population at risk
  • Making comparisons
  • Developing the hypothesis
  • Testing the hypothesis
  • Making scientific inferences
  • Conducting experimental studies
  • Intervening and evaluating

Evidence Based Chronic Disease Prevention

surveillance
Surveillance
  • Public health surveillance is the ongoing systematic collection, analysis, and interpretation of health data essential to the planning, implementation and evaluation of public health practice, closely integrated with the timely dissemination of these data to those who need to know.
  • 3 Purposes to surveillance
    • identify public health problems
    • stimulate public health intervention
    • suggest hypotheses for epidemiologic research

Evidence Based Chronic Disease Prevention

surveillance cycle
Surveillance Cycle
  • Collection of data
    • Pertinent, Standardized, Regular, Frequent, Timely
  • Consolidation and interpretation
    • Orderly, Descriptive, Evaluative, Timely
  • Dissemination
    • Prompt, All who need to know (data providers, action takers)
  • Action to control and prevent

Evidence Based Chronic Disease Prevention

characteristics of a surveillance system
Characteristics of a Surveillance System
  • Simplicity-clear and easily understood
  • Acceptability- straightforward (non-political)
  • Sensitivity-ability to correctly detect problem
  • High predictive value positive-persons reported to have condition under surveillance have high probability of having condition
  • Timeliness-data is promptly reported once collected
  • Flexibility-system is versatile and adaptable
  • Representativeness-correctly portrays health status of community

Evidence Based Chronic Disease Prevention

measures of disease frequency surveillance
Measures of Disease Frequency: Surveillance
  • Public health surveillance systems are important tools for collecting descriptive epidemiologic data.
  • Different surveillance collection methods provide varying levels of confidence in the data
    • Population-based -- complete reporting
    • Representative samples
    • Convenience samples

Evidence Based Chronic Disease Prevention

measures of disease frequency surveillance data
Vital statistics

Birth certificates (all states)

Death certificates (all states)

Sentinel surveillance

Infectious diseases (CDC)

Occupational diseases (OSHA)

Administrative data collection systems

Hospital discharge data (HIDI)

Health plan employer data & information set (HEDIS)

Registries

Cancers (SEER, most states)

Birth defects (CDC, some states)

Health surveys

Behavioral risk factor surveillance system (all states) and YBRFSS

National health & ambulatory care survey (NIH)

National health interview survey (NIH)

National health & nutritional examination survey (NIH)

National survey of family growth (NIH)

Measures of Disease Frequency: Surveillance Data

Evidence Based Chronic Disease Prevention

types of surveillance
Types of Surveillance
  • Passive
  • Active
  • Sentinel
  • Special systems

Evidence Based Chronic Disease Prevention

types of surveillance88
Types of Surveillance
  • Passive
    • most common in state/local health depts
    • uses standardized reporting cards/forms
    • collect data from clinics, hospitals, laboratories
    • targets physicians, laboratories, ICPs
    • completeness of reporting - lowest
    • least expensive to maintain
    • passive - no action taken unless completed reports received by public health agency

Evidence Based Chronic Disease Prevention

types of surveillance89
Types of Surveillance
  • Active
    • ongoing search for cases
    • involves regular contacts with key reporting sources (calls to MDs, labs)
    • frequent review of data for cases of specific condition
    • high levels of completeness of reporting
    • more expensive to maintain

Evidence Based Chronic Disease Prevention

types of surveillance90
Types of Surveillance
  • Sentinel systems
    • involve use of sample of providers (MD practices, ER)
    • identify trends in disease that occur at relatively high frequency (influenza)
    • less useful for disease that require follow-up to intervene to prevent spread (Hepatitis A)
      • Sentinel health event
        • case of unnecessary disease, unnecessary disability or untimely death whose occurrence is a warning signal that the quality of preventive or medical care may need to be improved

Evidence Based Chronic Disease Prevention

types of surveillance91
Types of Surveillance
  • Special systems
    • Useful for specific types of surveillance
    • BRFSS - identify trends in behavior that affect health risk
    • KAB surveys - identify impact of public health education efforts (HIV/AIDS)
    • Microbiologic surveys - determine prevalence of antibiotic resistance of persons with invasive infections like pneumonia, presence of cholera in sewage
    • Hospital discharge data - trends in dx/conditions requiring hospitalization

Evidence Based Chronic Disease Prevention

final comments
Final Comments
  • Public health practitioners and political leaders do not have the luxury of waiting around for irrefutable evidence to surface
  • Decisions on public health resources, policies and interventions must be made
  • These decisions should be made, however, based on available scientific evidence, particularly analytic epidemiologic evidence

Evidence Based Chronic Disease Prevention

other on line resources
Other On-line Resources
  • World Wide Web Virtual Library Epidemiology
    • http://www.epibiostat.ucsf.edu/epidem/epidem.html
  • Supercourse, Epidemiology the Internet and Global Health (CDC co-sponsors)
    • http://www.pitt.edu/~super1/
  • CDC Epidemiology Program Office
    • http://www.cdc.gov/epo/
  • American College of Epidemiology
    • http://www.acepidemiology.org/
  • Epi Info and Epi Map
    • http://www.cdc.gov/epiinfo/
  • World Wide Web Geographic Information Systems (GIS)
    • http://www.geo.ed.ac.uk/home/giswww.html

Evidence Based Chronic Disease Prevention