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 57

April 6, 2009 58

April 6, 2009 59

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 6813/7/2008 68

# deaths in Canada from 1979-2004; men and women.

April 6, 2009 6913/7/2008 69

Mortality RATES in Canada from 1979-2004; men and women.

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 74

Sex ratio (M/F) in Canada from 1979-2004.

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 77

PYLL’s for various conditions, 2001

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 83

April 6, 2009 84

Overall trends in mortality from Cancer 1976-2005:rates and numbers

April 6, 2009 85

Overall trends in mortality 1976-2005: rates and numbers

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