april 6, 20091 back to basics, 2009 population health (1): general objectives n birkett, md...
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April 6, 2009 1
Back to Basics, 2009POPULATION HEALTH (1):
GENERAL OBJECTIVESN Birkett, MD
Epidemiology & Community Medicine
Based on slides prepared by Dr. R. SpasoffOther resources available on Individual & Population Health web site
April 6, 2009 2
THE PLAN
• We will follow MCC Objectives for Qualifying Examination (in italics)
• Focus is on topics not well covered in the Toronto Notes (UTMCCQE)
• Three sessions: General Objectives & Infectious Diseases, Clinical Presentations, Additional Topics
April 6, 2009 3
THE PLAN(2)
• First class– mainly lectures
• Other classes– About 1.5-2 hours of lectures– Review MCQs for 60 minutes
• A 10 minute break about half-way through• You can interrupt for questions, etc. if
things aren’t clear.
April 6, 2009 4
THE PLAN (3)
• Session 1 (April 6, 1300-1600)– Diagnostic tests
• Sensitivity, specificity, validity, PPV
– Health Promotion
– Critical Appraisal (more on April 7)
– Elements of Health Economics
– Vital Statistics
– Overview of Communicable Disease control, epidemics, etc.
April 6, 2009 5
THE PLAN (4)
• Session 2 (April 4, 1300-1600)– Clinical Presentations
• Periodic Health Examination• Immunization• Occupational Health• Health of Special Populations• Disease Prevention• Determinants of Health• Environmental Health
April 6, 2009 6
THE PLAN (5)
• Session 3 (April 9, 1300-1600)– CLEO
• Overview of Ethical Principles
• Organization of Health Care Delivery in Canada
– Other topics• Intro to Biostatistics
• Brief overview of epidemiological research methods
April 6, 2009 7
LMCC New Objectives (1)
Population Health• Concepts of Health and Its Determinants (78-1)• Assessing and Measuring Health Status at the
Population Level (78-2)• Interventions at the Population Level (78-3)• Administration of Effective Health Programs at
the Population Level (78-4)• Outbreak Management (78-5)• Environment (78-6)• Health of Special Populations (78-7)
April 6, 2009 8
LMCC New Objectives (2)
C2LEO (URL to LMCC objective page)
• Considerations for – Cultural-Communication, Legal, Ethical and
Organizational Aspects of the Practice of Medicine
April 6, 2009 9
LMCC New Objectives (3)
• We won’t be able to cover every objective in detail.
• Sessions will be based around objectives, with links identified as appropriate.
• Start with some overviews.
April 6, 2009 10
LMCC New Objectives (4)
78.1: CONCEPTS OF HEALTH AND ITS DETERMINANTS
• Define and discuss the concepts of health, wellness, illness, disease and sickness.
• Describe the determinants of health and how they affect the health of a population and the individuals it comprises.
• Lifecourse/natural history• Illness behaviour• Culture and spirituality
April 6, 2009 11
LMCC New Objectives (5)
78.1: CONCEPTS OF HEALTH AND ITS DETERMINANTS• Determinants of health include:
– Income/social status– Social support networks– Education/literacy– Employment/working conditions– Social environments– Physical environments– Personal health practices/coping skills– Healthy child development– Biology/genetic endowment– Health services– Gender– Culture
April 6, 2009 12
LMCC New Objectives (6)
78.2: ASSESSING AND MEASURING HEALTH STATUS AT THE POPULATION LEVEL
• Describe the health status of a defined population.
• Measure and record the factors that affect the health status of a population with respect to the principles of causation
– Principles of Epidemiology, critical appraisal, causation, etc.
April 6, 2009 13
LMCC New Objectives (7)
78.3: INTERVENTIONS AT THE POPULATION LEVEL
• Understand three levels of prevention
• Concepts of Health Promotion, etc.
• Role of physicians at the community level.
• Impact of public policy
April 6, 2009 14
LMCC New Objectives (8)
78.4: ADMINISTRATION OF EFFECTIVE HEALTH PROGRAMS AT THE POPULATION LEVEL
• Structure of the Canadian Health Care System
• Concepts of economic evaluation
• Quality of care assessment
April 6, 2009 15
LMCC New Objectives (9)
78.5: OUTBREAK MANAGEMENT
• Know defining characteristics of an outbreak
• Demonstrate essential skills in outbreak control
April 6, 2009 16
LMCC New Objectives (10)
78.6: ENVIRONMENT• Recognize implications of environmental
health at the individual and community levels• Know methods of information gathering• Work collaboratively with other groups• Recommend to patients and groups how they
can minimize risk and maximize overall function
April 6, 2009 17
LMCC New Objectives (11)
78.7: HEALTH OF SPECIAL POPULATIONS• Specific target population include:
– First Nations, Inuit, Métis Peoples
– Global health and immigration
– Persons with disabilities
– Homeless persons
– Challenges at the extremes of the age continuum
April 6, 2009 18
LMCC New Objectives (12)
C2LEO
• Same material as before but re-structured.
• Read objectives for the details
April 6, 2009 19
Getting Started
• We can’t cover everything.• Will concentrate on topics not well covered in the
Toronto notes and material of greatest importance.• Material will ‘jump around’ a bit
– Slides were based on previous LMCC objectives. I didn’t get new objectives until the week before these lectures. Hence, material won’t flow by LMCC objectives but rather by content links.
April 6, 2009 20
INVESTIGATIONS (1)
• 78.2– Determine the reliability and predictive value of
common investigations– Applicable to both screening and diagnostic
tests.
April 6, 2009 21
Reliability
• = reproducibility. Does it produce the same result every time?
• Related to chance error
• Averages out in the long run, but in patient care you hope to do a test only once; therefore, you need a reliable test
April 6, 2009 22
Validity
• Whether it measures what it purports to measure in long run, viz., presence or absence of disease
• Normally use criterion validity, comparing test results to a gold standard
• Link to I&PH web on validity
April 6, 2009 23
Reliability and Validity: the metaphor of target shooting. Here, reliability is represented by consistency, and validity by aim
Reliability Low High
Low
Validity
High
•
••
•
•
•
•
• •
••
•
•••
•••
•• ••••
April 6, 2009 24
Gold Standards
• Possible gold standards:– More definitive (but expensive or invasive) test– Complete work-up– Eventual outcome (for screening tests, when
workup of well patients is unethical; in clinical care you cannot wait)
• First two depend upon current state of knowledge and available technology
April 6, 2009 25
Test Properties (1)Diseased Not diseased
Test +ve 90 5 95
Test -ve 10 95 105
100 100 200
True positives False positives
False negatives True negatives
April 6, 2009 26
Test Properties (2)Diseased Not diseased
Test +ve 90 5 95
Test -ve 10 95 105
100 100 200
Sensitivity = 0.90 Specificity = 0.95
April 6, 2009 27
2x2 Table for Testing a Test
Gold standard
Disease Disease
Present Absent
Test Positive a (TP) b (FP)
Test Negative c (FN) d (TN)
Sensitivity Specificity
= a/(a+c) = d/(b+d)
April 6, 2009 28
Test Properties (6)• Sensitivity =Pr(test positive in a person
with disease)• Specificity = Pr(test negative in a person
without disease)• Range: 0 to 1
– > 0.9: Excellent– 0.8-0.9: Not bad– 0.7-0.8: So-so– < 0.7: Poor
April 6, 2009 29
Test Properties (7)
• Values depend on cutoff point
• Generally, high sensitivity is associated with low specificity and vice-versa.
• Not affected by prevalence, if severity is constant
• Do you want a test to have high sensitivity or high specificity?– Depends on cost of ‘false positive’ and ‘false negative’
cases
– PKU – one false negative is a disaster
– Ottawa Ankle Rules
April 6, 2009 30
Test Properties (8)
• Sens/Spec not directly useful to clinician, who knows only the test result
• Patients don’t ask: if I’ve got the disease how likely is it that the test will be positive?
• They ask: “My test is positive. Does that mean I have the disease?”
• Predictive values.
April 6, 2009 31
Test Properties (9)Diseased Not diseased
Test +ve 90 5 95
Test -ve 10 95 105
100 100 200
PPV = 0.95
NPV = 0.90
April 6, 2009 32
2x2 Table for Testing a Test
Gold standard
Disease Disease
Present Absent
Test + a (TP) b (FP) PPV = a/(a+b)
Test - c (FN) d (TN) NPV= d/(c+d)
a+c b+d
April 6, 2009 33
Predictive Values
• Based on rows, not columns
– PPV = a/(a+b); interprets positive test
– NPV = d/(c+d); interprets negative test
• Depend upon prevalence of disease, so must be determined for each clinical setting
• Immediately useful to clinician: they provide the probability that the patient has the disease
April 6, 2009 34
Prevalence of Disease
• Is your best guess about the probability that the patient has the disease, before you do the test
• Also known as Pretest Probability of Disease
• (a+c)/N in 2x2 table
• Is closely related to Pre-test odds of disease: (a+c)/(b+d)
April 6, 2009 35
Test Properties (10)Diseased Not diseased
Test +ve a b a+b
Test -ve c d c+d
a+c b+d a+b+c+d =N
odds
prevalence
April 6, 2009 36
Prevalence and Predictive Values
• Predictive values for a test dependent on the pre-test prevalence of the disease
– Tertiary hospitals see more pathology then FP’s; hence, their tests are more often true positives.
• How to ‘calibrate’ a test for use in a different setting?
• Relies on the stability of sensitivity & specificity across populations.
April 6, 2009 37
Methods for Calibrating a Test
Four methods can be used:– Apply definitive test to a consecutive series of
patients (rarely feasible)– Hypothetical table– Bayes’s Theorem– Nomogram
You need to be able to do one of the last 3. By far the easiest is using a hypothetical table.
April 6, 2009 38
Calibration by hypothetical table
Fill cells in following order:
“Truth”
Disease Disease Total PV
Present Absent
Test Pos 4th 7th 8th 10th
Test Neg 5th 6th 9th 11th
Total 2nd 3rd 1st (10,000)
April 6, 2009 39
Test Properties (12)
Diseased Not diseased
Test +ve 425 50 475
Test -ve 75 450 525
500 500 1,000
Tertiary care: research study. Prev=0.5
PPV = 0.89
Sens = 0.85 Spec = 0.90
April 6, 2009 40
Test Properties (13)
Diseased Not diseased
Test +ve
Test -ve
10,000
Primary care: Prev=0.01
PPV = 0.08
9,900
85
15
100
990
8,910
1,075
8,925
0.01*10000
0.85*100
0.9*9900
April 6, 2009 41
Calibration by Bayes’ Theorem
• You don’t need to learn Bayes’ theorem
• Instead, work with the Likelihood Ratio (+ve).
April 6, 2009 42
Test Properties (9)Diseased Not
diseased
Test +ve
90 5 95
Test -ve
10 95 105
100 100 200 Pre-test odds = 1.00
Post-test odds = 18.0
Likelihood ratio (+ve) = LR(+) = 18.0/1.0 = 18.0
April 6, 2009 43
Calibration by Bayes’s Theorem
• You can convert sens and spec to likelihood ratios– LR+ = sens/(1-spec)
LR+ is fixed across populations just like sensitivity & specificity.
• Bigger is better.• Posttest odds = pretest odds * LR+
– Convert to posttest probability if desired…
April 6, 2009 44
Calibration by Bayes’s Theorem
• How does this help?• Remember:
– Post-test odds = pretest odds * LR (+)
• To ‘calibrate’ your test for a new population:– Use the LR+ value from the reference source
– Compute the pre-test odds for your population
– Compute the post-test odds
– Convert to post-test probability to get PPV
April 6, 2009 45
Converting odds to probabilities
• Pre-test odds = prevalence/(1-prevalence)– if prevalence = 0.20, then pre-test odds
= .20/0.80 = 0.25
• Post-test probability = post-test odds/(1+post-test odds)
– if post-test odds = 0.25, then prob = .25/1.25 = 0.2
April 6, 2009 46
Example of Bayes’s Theorem(‘new’ prevalence 1%, sens 85%, spec 90%)
• LR+ = .85/.1 = 8.5 (>1, but not that great)
• Pretest odds = .01/.99 = 0.0101
• Positive Posttest odds = .0101*8.5 = .0859
• PPV = .0859/1.0859 = 0.079 = 7.9%
• Compare to the ‘hypothetical table’ method (PPV=8%)
April 6, 2009 47
Calibration with Nomogram
• Graphical approach avoids some arithmetic• Expresses prevalence and predictive values
as probabilities (no need to convert to odds)• Draw lines from pretest probability
(=prevalence) through likelihood ratios; extend to estimate posttest probabilities
• Only useful if someone gives you the nomogram!
April 6, 2009 48
Example of Nomogram (pretest probability 1%, LR+ 45, LR– 0.102)
Pretest Prob. LR Posttest Prob.
1%45
.10231%
0.1%
April 6, 2009 49
INVESTIGATIONS (2)State the effect of demographic considerations on the
sensitivity and specificity of diagnostic tests
• Generally, assumed to be constant. BUT…..• Sensitivity and specificity usually vary with
severity of disease, and may vary with age and sex • Therefore, you can use sensitivity and specificity
only if they were determined on patients similar to your own
• Spectrum bias
April 6, 2009 50
The Government is extremely fond of amassinggreat quantities of statistics. These are raised to the nth degree, the cube roots are extracted, and
the results are arranged into elaborate and impressive displays. What must be kept ever in
mind, however, is that in every case, the figures are first put down by a village watchman, and he puts
down anything he damn well pleases!
Sir Josiah Stamp,Her Majesty’s Collector of Internal Revenue.
April 6, 2009 51
78.3: HEALTH PROMOTION & MAINTENANCE (1)
• Definitions of health
• Concepts of Health Promotion
April 6, 2009 52
Definitions of Health
1. A state of complete physical, mental and social well-being and not merely the absence of disease or infirmity. [The WHO, 1948]
2. A joyful attitude toward life and a cheerful acceptance of the responsibility that life puts upon the individual [Sigerist, 1941]
3. The ability to identify and to realize aspirations, to satisfy needs, and to change or cope with the environment. Health is therefore a resource for everyday life, not the objective of living. Health is a positive concept emphasizing social and personal resources, as well as physical capacities. (WHO Europe, 1986]
April 6, 2009 53
HEALTH PROMOTION
• Distinct from disease prevention.
• Focuses on ‘health’ rather than ‘illness’
• Broad perspective. Concerns a network of issues, not a single pathology.
• Participatory approach. Requires active community involvement.
• Partnerships with NGO’s, NPO’s, etc.
April 6, 2009 54
HEALTH PROMOTION
• Ottawa Charter for Health Promotion (1996)
• Five key pillars to action:– Build Healthy Public Policy– Create supportive environments– Strengthen community action– Develop personal skills– Re-orient health services
April 6, 2009 55
HEALTH PROMOTION• Health Education
– Health Belief model– Stages of Change model
• Risk reduction strategies• Social Marketing• Healthy public policy
– Tax policy to promote healthy behaviour– Anti-smoking laws, seatbelt laws– Affordable housing
April 6, 2009 56
78.1: Illness Behaviour
• “Describe the concept of illness behaviour and its influence on health care”
• Utilization of curative services, coping mechanisms, change in daily activities
• Patients may seek care early or may delay (avoidance, denial)
• Adherence may increase or decrease
April 6, 2009 60
78.2: CRITICAL APPRAISAL (1)
• “Evaluate scientific literature in order to critically assess the benefits and risks of current and proposed methods of investigation, treatment and prevention of illness”
• Most will be covered in session on April 9• UTMCCQE does not present hierarchy of
evidence (e.g., as used by Task Force on Preventive Health Services)
April 6, 2009 61
Hierarchy of evidence(lowest to highest quality, approximately)
• Expert opinion• Case report/series• Ecological (for individual-level exposures)• Cross-sectional• Case-Control• Historical Cohort• Prospective Cohort• Quasi-experimental• Experimental (Randomized)
}similar/identical
April 6, 2009 62
78.1: MEDICAL ECONOMICS (1)
• Define the socio-economic rationales, implications and consequences of medical care
• Medical care costs society financial and other resources.
• This objective aims to raise awareness of these types of issues.
April 6, 2009 63
MEDICAL ECONOMICS (2)
• Is there a net financial benefit from medical care?
• How do we value non-fiscal benefits such as quality of life, ‘health’, not being dead?
• Should resources be spent on health or other societal objectives?
• How do we value non-traditional expenditures, etc which impact on health (Healthy Public Policy).
April 6, 2009 64
MEDICAL ECONOMICS (3)
• “Outline the principles of cost-containment, cost benefit analysis and cost effectiveness”
• Not addressed in UTMCCQE
April 6, 2009 65
Principles of cost-containment
• Eliminate ineffective care• Reduce costs of effective care
– Substitute cheaper but equally effective care,• day surgery for hospital admission, • nurse practitioners for some primary care, • generic drugs
– Reduce unit costs• reduce salaries (risk of reduced effectiveness) or
fees (but quantity provided may increase)
April 6, 2009 66
Types of economic analysis
[Costs always expressed in dollars]
• Cost-minimization: assume equal outcomes
• Cost-benefit: outcomes in dollars
• *Cost-effectiveness: outcomes in natural units (deaths, days of care or disability, etc.)
• *Cost-utility: outcomes in QALYs (quality-adjusted life years)
April 6, 2009 67
78.1: VITAL STATISTICS INFORMATION
• What are the key causes of illness or death in Canada? Common things are common – using epidemiology can help you run a better clinical practice
• How have disease incidence and mortality change in Canada in the past 20 years?– Little good information on disease incidence
except for cancer (cancer registries)
April 6, 2009 70
VITAL STATISTICS (2)
• Leading causes of death– ‘Cardiovascular disease’: 37%
• Heart disease: 20%• ‘Other circulatory disease’: 10%• ‘Stroke’ 7%
– ‘Cancer’: 28%• Lung cancer: 9% (M); 6% (W)• Breast cancer: 4% (W)• Prostate cancer: 4% (M)
– Respiratory Disease: 10%– Injuries: 6%– Diabetes: 3%– Alzheimer’s: 1%
April 6, 2009 71
Mortality (2004) - Canada, both sexesAge standardized: 1991 population
Stroke (6.1%)
IHD (16.1%)
CHD:other (5.4%)Cancer: Lung (8.1%)
Cancer: Colon (3.3%)
Cancer: Breast (2.2%)
Cancer: Other (16.7%)
Accidents:MVA (1.5%)
Accidents:Other (2.8%)
Diabetes (3.5%)
Infections (1.2%)
Respiratory (6.7%)
Other (21.8%)
Alzheimer's (2.2%)Suicide (1.9%)
CANCER: 30.3%
Circ Disease:27.6%
†††
† Pneumonia & influenza grouped with respiratory disease. Would increase infectious % to about 3.4%.
April 6, 2009 72
Mortality (2004) - Canada, MEN onlyAge standardized: 1991 population
Stroke (5.3%)
IHD (18.8%)
CHD:other (4.9%)Cancer: Lung (8.5%)
Cancer: Colon (3.3%)
Cancer: Prostate (3.3%)
Cancer: Other (14.7%)
Accidents:MVA (1.8%)
Accidents:Other (3.0%)
Diabetes (3.5%)
Infections (1.1%)
Respiratory (7.2%)
Other (20.8%)
Alzheimer's (1.5%)Suicide (2.3%)
CANCER: 29.8%
Circ Disease:29.0%
††
† Pneumonia & influenza grouped with respiratory disease. Would increase infectious % to about 3.5%.
April 6, 2009 73
Mortality (2004) - Canada, WOMEN onlyAge standardized: 1991 population
Stroke (7.0%)
IHD (14.5%)
CHD:other (5.8%)Cancer: Lung (7.8%)
Cancer: Colon (3.2%)
Cancer: Breast (5.0%)
Cancer: Other (15.6%)
Accidents:MVA (1.0%)
Accidents:Other (2.4%)
Diabetes (3.4%)
Infections (1.0%)
Respiratory (6.5%)
Other (22.7%)
Alzheimer's (2.9%)Suicide (1.1%)
CANCER: 31.6%
Circ Disease:27.3%
††
† Pneumonia & influenza grouped with respiratory disease. Would increase infectious % to about 3.3%.
April 6, 2009 75
Age/sex-specific Mortality.Canada, 2005
Age at death (years)
0 20 40 60 80
Rat
e/10
0,00
0
0
2000
4000
6000
8000
10000
12000
14000CombinedMalesFemales
April 6, 2009 76
Age-specific mortality: male:female mortality ratioCanada, 2005
1.0=same mortality in both sexes; > 1.0 -> higher male mortality
Age (years)
0 20 40 60 80
Rat
io (
M:F
)
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
April 6, 2009 78
Injury Mortality in Canada, 2004
Age at death (years)
0 20 40 60 80
Rat
e/10
0,00
0
0
50
100
150
200
250
300
350
Total MVA FallsSuffocation Other unintentional Suicide Homicide
April 6, 2009 79
Injury Mortality in Canada, 2004Excluding poeple over age 80
Age at death (years)
0 20 40 60 80
Rat
e/10
0,00
0
0
10
20
30
40
50
60
70
Total MVA FallsSuffocation Other unintentional Suicide Homicide
April 6, 2009 80
Pattern of Injury deaths, Canada, 2004Age 1 to 10.
MVA FallsSuffocationOther unintentionalHomicide
April 6, 2009 81
Pattern of Injury deaths, Canada, 2004Age 80 and over.
MVAFallsSuffocationOther unintentionalSuicideHomicde
April 6, 2009 82
Vital Stats (3)
• In the USA, it is estimated that 86,000 people are sent to ER every year after a fall caused by a cat or dog!– Mainly minor injuries but 10% are fractures,
internal bleeding, etc.– Cats mainly trip people by walking under your
feet.– Dogs (the main source of injuries!) causes trips,
push people over or pull them over on walks.
• Watch out!!
April 6, 2009 86
Cancer and AgeAge-Specific Incidence Rates for All Cancers by Sex, Canada, 2003
Surveillance Division, CCDPC, Public Health Agency of Canada
April 6, 2009 87
Cancer and AgeAge-Specific Mortality Rates for All Cancers by Sex, Canada, 2003
Surveillance Division, CCDPC, Public Health Agency of Canada
April 6, 2009 88
Time trends in incidence - Males
Age-Standardized Incidence Rates (ASIR) for Selected Cancer Sites, Males, Canada, 1978-2007
Surveillance and Risk Assessment Division, CCDPC, Public Health Agency of Canada
1975 1980 1985 1990 1995 2000 2005
0
20
40
60
80
100
120
140
160
Prostate
Lung
Colorectal
Bladder
NHLStomach
Melanoma
Larynx
Liver
Thyroid
Estimated
April 6, 2009 89
1980 1985 1990 1995 2000 2005
AS
MR
(/1
00
,00
0)
0
20
40
60
80
100
Prostate
Lung
Colorectal
NHL
Stomach
Oral
Larynx
Hodgkin's
Time trends in mortality - Males
Age-Standardized Incidence Rates (ASIR) for Selected Cancer Sites, Males, Canada, 1978-2007
Surveillance and Risk Assessment Division, CCDPC, Public Health Agency of Canada
Estimated
April 6, 2009 90
1975 1980 1985 1990 1995 2000 2005
0
20
40
60
80
100
120
140
160
Breast
Lung
Colorectal
NHLStomach
Cervix
Larynx
Thyroid
Time trends in incidence - Females
Age-Standardized Incidence Rates (ASIR) for Selected Cancer Sites, Females, Canada, 1978-2007
Surveillance and Risk Assessment Division, CCDPC, Public Health Agency of Canada
Estimated
April 6, 2009 91
1980 1985 1990 1995 2000 2005
AS
MR
(/1
00,
000)
0
20
40
60
80
100
Breast
Lung
Colorectal
NHL
Stomach
Cervix
Time trends in mortality - Females
Age-Standardized Incidence Rates (ASIR) for Selected Cancer Sites, females, Canada, 1978-2007
Surveillance and Risk Assessment Division, CCDPC, Public Health Agency of Canada
Estimated