measuring the occurrence of disease 1 sue lindsay, ph.d., msw, mph division of epidemiology and...
TRANSCRIPT
![Page 1: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/1.jpg)
Measuring the Occurrence of Disease 1
Sue Lindsay, Ph.D., MSW, MPH
Division of Epidemiology and Biostatistics
Institute for Public Health
San Diego State University
![Page 2: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/2.jpg)
Pandemic Preparedness
www.readysandiego.org
http://www.ready.gov
![Page 3: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/3.jpg)
Types of Measurement Commonly Used in Epidemiology
• Proportions
• 25 males/50 people = 0.50 or 50%
• Rates
• number of cases/population, cohort, or sample
• a specified time period
• all in the denominator have the potential to be in the numerator
• Ratios
• An expression of the relationship between numerator and
denominator where they are two separate and distinct
quantities: 25 females/29 males
![Page 4: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/4.jpg)
Common Sources of Data For Stages in the Natural History of Disease
Disease
Onset
Symptoms Seek
Care
Diagnosis/
Treatment
Healthy
Interviews
Medical RecordsSources
Of Data }
Outcome
Surveys
Birth Records
Death Records
![Page 5: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/5.jpg)
Measures of Morbidity
• Point Prevalence
• Period Prevalence
• Incidence
• Cumulative incidence
• Incidence density
• Lifetime incidence
![Page 6: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/6.jpg)
Types of Populations
• Dynamic Population
• Fixed Population
![Page 7: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/7.jpg)
Point Prevalence
Prevalence
Per 1,000=
No. of Existing Cases of Disease
In a Population
No. of Persons in the Population
At a Specific Point in TimeExpressed as either a rate or percentage
![Page 8: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/8.jpg)
Period Prevalence
Prevalence
Per 1,000=
No. of Existing Cases of Disease
In a Population
No. of Persons in the Population
During a Specified Period of Time
Expressed as a rate: 50/10,000 persons in City A have diabetes in 2007
![Page 9: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/9.jpg)
Incidence
Incidence
Per 1,000=
No. of New Cases of Disease
In a Population
No. of Persons at Risk of
Developing Disease
During a Specified Period of Time
Expressed as a rate: 10 persons/10,000 developed new diabetes in 2007
![Page 10: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/10.jpg)
Cumulative Incidence
No. of New Cases of Disease in a Time Period
Number of persons in the population
Expressed as a percentage:
2% of the 500,000 persons in City A developed diabetes in 2007
![Page 11: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/11.jpg)
Lifetime Incidence(lifetime cumulative incidence)
No. of New Cases of Disease in a Time Period
Number of persons in the population
Expressed as a percentage:
20% of the persons in City A developed diabetes in their lifetimes
![Page 12: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/12.jpg)
Fixed Populations
(study populations)
![Page 13: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/13.jpg)
Incidence Density
No. of New Cases of Disease in a Time Period
Person-time at risk for the same time period
![Page 14: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/14.jpg)
Calculation of Person-Time
Example:
10 people followed for 3 years =
30 person-years or 360 person-months
3 people followed for 10 years =
30 person-years or 360-person months
![Page 15: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/15.jpg)
Example Calculations
0 1 2 3 4
1
2
3
4
5
6
7
8
Studysubjects
• Incidence rate = 5/8 = 62.5/100 in 3 years• Incidence density = 5/18 person-years at risk
= 5/18 = 27.8/100 person-years• Prevalence in year 2 = 3/6 = 50/100
Time (years)
Patient died
Patient lost to follow-up Red = disease
Green= no disease
![Page 16: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/16.jpg)
Incidence: Important Concepts
• Incidence is a measure of the risk of disease!
• As incidence goes up, so does risk
• The numerator is only NEW cases of disease
• The denominator must include only those persons at risk for developing the disease
• Time unit must be clearly specified
• All persons at risk must be followed the entire time period
![Page 17: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/17.jpg)
Uterine Cancer Incidence Rates, Alameda County
Years
Rat
e P
er 1
00,0
00
0
10
20
30
40
50
60
70
80
1960 1965 1970 1975
all women
only women withouthysterectomy
![Page 18: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/18.jpg)
Differences BetweenIncidence and Prevalence
• Prevalence is only a snapshot of the population at a point or period in time - who has the disease and who does not
• Prevalence tells you nothing about how long patients have had the disease in the population
• Incidence includes only new cases or events among those at risk, and is a measure of risk of disease
![Page 19: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/19.jpg)
Factors that Affect Prevalence:
• Prevalence rates are increased by:
• Immigration of cases or those with a high potential to become cases (elderly)
• Emigration of healthy individuals
• Increases in the duration of the disease
(earlier detection, better treatment, reduced fatality, etc.)
• Increases in incidence (occurrence of new cases)
![Page 20: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/20.jpg)
Factors that Affect Prevalence:
• Prevalence rates are decreased by:• Immigration of healthy persons • Emigration of persons with disease• Improved cure rates• Increased death rates• Decreases in incidence (occurrence of new
cases)• Shorter duration of the disease
![Page 21: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/21.jpg)
Examples of Point and Period Prevalence, Incidence, and Cumulative Incidence
• Do you currently have asthma?
• Have you had asthma during the last year?
• Did you have your first episode of asthma this year?
• Have you ever had asthma?
• Point Prevalence
• Period Prevalence
• Incidence
• Cumulative or Lifetime Incidence
![Page 22: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/22.jpg)
The Relationship Between Incidence and Prevalence
Prevalence = Incidence x Duration
![Page 23: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/23.jpg)
Low incidence and long duration
Incidence
Low Risk
N = 4/yr.
Duration
Long
25 Yrs
(25 X 4) Prevalence
100/1,000
![Page 24: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/24.jpg)
High incidence and short duration
Incidence
High Risk
N = 20/yr.
Duration
Short
3 Yrs
(20 X 3) Prevalence
60/1,000
![Page 25: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/25.jpg)
Prevalence of Coronary Heart Disease (CHD) Among 4,469 Persons, Framingham Study
0
5
10
15
20
25
30
35
40
45
50
30-44 45-62
Men
Women
Rat
e P
er 1
,000
Age
![Page 26: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/26.jpg)
Incidence of Coronary Heart Disease (CHD) Among 4495 Persons,
Framingham Study
0
20
40
60
80
100
120
140
30-39 40-49 50-59
Men
WomenR
ate
Per
1,0
00
Age
![Page 27: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/27.jpg)
General Sources of Morbidity Statistics
Disease
Reporting
Hospitals and
Clinics
Case-finding
Programs
Insurance
Absenteeism
Records
Military Service
Tax-Financed Medical Care
Physical Exams in Industry
Morbidity Surveys
![Page 28: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/28.jpg)
Sources of Morbidity Information About Cancer
Medical records
Hospital Discharge Data
Billing Records
Medicare
Cancer registries
SEER (Surveillance, Epidemiology, and End Results)
SEER/Medicare linked data sets
HEDIS (Health Plan Employer Data and Information Set)
![Page 29: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/29.jpg)
SEER
SEER – Surveillance, Epidemiology, and End Results
Summary of cancer registry data from 4 states and 5 large metropolitan areas
Represents 10% US population
Used to estimate cancer rates for the nation
![Page 30: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/30.jpg)
HEDIS
Health Plan Employer Data and Information Set
Established by National Committee for Quality Assurance
Quality measures to compare health insurance plans
![Page 31: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/31.jpg)
Incidence and Prevalence: Challenges with the Numerator
• Who has the disease?• Diagnostic criteria can strongly impact rates
• Can be differences in case definitions
• Case definitions may change over time
• There may be changes in the quality of screening services
• Who Should Be Counted? • Is case finding accurate and inclusive? How large is the
effort to find all cases?
• Case finding by interview may yield inaccurate counts
![Page 32: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/32.jpg)
PREVALENCE OF DEMENTIA BY DIFFERING CRITERIA
0
5
10
15
20
25
30
DSM-III DSM-IIIR DSM-IV ICD-9 ICD-10 CAMDEX CLINCONS
CRITERIA
PR
EV
AL
EN
CE
%
![Page 33: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/33.jpg)
Number of Cases of Rape
0
200,000
400,000
600,000
800,000
Nu
mb
er
of
Ra
pe
s
97,47097,470
260,300260,300
683,000683,000
US Dept. of JusticeBureau of Justice Statistics
(NCVS) 1995
National Women’s Study1990
FBI Uniform CrimeReport for 1995
![Page 34: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/34.jpg)
AIDS CASES BY YEAR, 1984 - 1993
0
5
10
15
20
25
30
35
40
1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
Years
Th
ou
san
ds
of
Cas
es
![Page 35: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/35.jpg)
SOURCES OF ERROR IN INTERVIEW SURVEYS
• Patient:
• Unaware of Disease
• Misunderstanding of Diagnosis
• Inaccurate Recall
• Refusal to Respond
• Altering of Response
• Interviewer :
• Interviewer Bias
• Selection of Subjects
• Lack of standardization of interview format
![Page 36: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/36.jpg)
Limitations of Hospital Data Sources
• Admissions are selective
• Hospital records are not designed for research
• The denominator or population at risk is usually not known
![Page 37: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/37.jpg)
Incidence and Prevalence:Problems with the Denominator
• Selective Undercounting – Who doesn’t get counted?
• Census Geographic Boundary changes
• Changes in Defined Populations Over Time
![Page 38: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/38.jpg)
Surveillance
A comprehensive system designed for the on-going detection and monitoring of the occurrence of health-related events or exposures in a target population
![Page 39: Measuring the Occurrence of Disease 1 Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State](https://reader035.vdocuments.us/reader035/viewer/2022062720/56649f055503460f94c19ac0/html5/thumbnails/39.jpg)
Key Features of Surveillance
• Continuous data collection and evaluation
• An identified target population
• A standard definition of the outcome of interest
• Emphasis on timeliness of collection and dissemination of results
• Use of data for purposes of disease investigation or control