Chapter 12 Clinical Epidemiology - PowerPoint Presentation

Slide1

Chapter 12

Clinical EpidemiologySlide2

Chapter Objectives

Define clinical epidemiology

Understand various aspects of screening and diagnostic tests

Describe various measures for evaluating prognosis

Discuss potential biases and ways to avoid bias in evaluation of tests and treatmentsSlide3

Clinical Epidemiology

Clinical epidemiology

focuses on patients and the application of epidemiologic methods to assess the efficacy of screening, diagnosis, and treatment in

clinical settings

Used to identify the health consequences of employing a test or administering

a treatmentSlide4

Questions

About

Clinical Epidemiology

Who is most likely to participate in screening and diagnostic testing?

How accurate is the screening or diagnostic test?

If a treatment is efficacious, what proportion of patients benefit from the treatment?

What characterizes those who benefit and those who do not benefit from the treatment?

How much do patients benefit from a treatment?

What

are the risks associated

with screening, diagnostic testing,

or treatment?Slide5

Secondary Prevention

Health

screening

and

detection

activities used to

identify diseaseSlide6

Screening vs. Diagnostic Tests

in Cancer

Examples of screening methods

Pap test

Mammograms

Blood tests (e.g., PSA)

Fecal occult blood test (FOBT)

Biopsy

Small blood sample – leukemiaSlide7

Medical Screening

Used to suggest or detect disease among individuals in a population without signs or symptoms of the

health problemSlide8

Why do we do

screenings?

Screening is used to promote detection of diseases in their earliest stages, when treatment has the greatest chance of working, in order to reduce morbidity

and mortalitySlide9

Common Screening Tests

Papanicolaou test (Pap smear, Pap test, cervical smear, or smear test)

Mammogram

Clinical breast exam

Fecal occult blood test

Prostate-specific antigen

test

Blood pressure determination

Cholesterol level

Eye examination

Urinalysis

Tuberculin skin test

Beck Depression InventorySlide10

How does mass screening compare with selective screening?

Mass screening is not selective but involves application of screening tests to the

total population

Selective screening involves applying the screening tests to high

risk groupsSlide11

Screening Guidelines

1968 World Health

Organization

The

disease or condition being screened for should be a

major

medical problem

Acceptable treatment

should be available for individuals with diseases discovered in the

screening process

Access

to healthcare

facilities and services

for follow-up diagnosis and treatment for the discovered disease should

be available

The disease should have a

recognizable course

, with identifiable early and

latent stagesSlide12

Screening

Guidelines (cont’d)

A

suitable and effective test or examination

for the disease(s) should

be available

The

test and the testing process

should be acceptable to the

general population

The

natural history

of the disease or condition should be adequately understood, including the regular phases and course of

the disease

Policies, procedures, and threshold levels on tests should be determined in advance to establish

who should be referred

for further testing, diagnostics, and

possible treatment

The process should be

simple

enough to encourage large groups of persons

to participateSlide13

Evaluating Screening Guidelines

How can the application of epidemiology provide a means for evaluating screening guidelines

?

Descriptive

and analytic epidemiologic methods are useful for establishing

and understanding

Extent

of public

health problem

Efficacy of treatment

Access to health care

Natural course of disease

Efficacy of a screening or

diagnostic testSlide14

Validity, Reliability, and Yield

Validity

– How well the test actually measures what it is supposed

to measure

Reliability

– How well the test performs in use over time(its

repeatability)

Yield

– The

amount of screening the test can accomplish in a

time periodSlide15

Validity

Refers to the accuracy and trustworthiness of instruments, data, and findings

in research

Are the instruments that were used to measure something valid?

GRE

SAT

ACTSlide16

Two ways to view and

assess validity

Content validity – Achieved

when an instrument has appropriate content for measuring a complex concept or construct

If you walk out of a test and feel that it was unfair because it tapped too narrow a band of knowledge

Construct validity

– The

measures “get at” or actually measure what you are

actually studying

Does the Wechsler IQ test measure

intelligence?Slide17

Accuracy

The degree to which the measurement represents what it is intended to represent

Important influence on the

validity

Spring on a scale not calibrated correctly; the scale is off.Slide18

Measures of Validity

Sensitivity

– Ability

of the test to correctly identify those with

the disease

Specificity

– Ability

of the test to correctly identify those without

the disease

Overall accuracy

– Ability

of a test to predict the presence or absence of

a disease

PV

+

–

Proportion

of people with a positive test result who have

the disease

PV-

–

Proportion

of people with a negative test result who do not have

the diseaseSlide19

Likelihood Ratios

Two additional measures for appraising screening and

diagnostic evidence

Likelihood Ratio Positive

(LR+)

Likelihood Ratio Negative

(LR-) Slide20

Likelihood Ratios

Positive

– Level

of

confidence that

a person who obtains a score in the affected range truly does have the

health problem

Negative

– Confidence

that a score in the unaffected range comes from a person who truly does not have the

health problemSlide21

Prognosis

Prediction or forecast of the course of a disease based on anticipation from the usual natural history of the disease or peculiarities unique to

the case

Prognostic indicators

tell

the doctor the likely behavior of the cancer and its responsiveness

to treatmentSlide22

Measures of Prognosis

Case fatality rate

– Proportion

of newly diagnosed cases that die from a given disease in a

specified period

Survival rate

– Proportion of

persons surviving,

regardless of cause

of deathSlide23

Cox Proportional Hazards

Regression Model

Useful for analyzing

survival data

Indicates the probability that a person will experience

an event

Estimate

the relative risk, adjusted for potential prognostic factors, thereby minimizing the threat

of confoundingSlide24

Lead Time Bias

Lead Time

– Difference

in time between the date of diagnosis with screening and the date of diagnosis

without screening

Lead Time Bias

– When lead time is counted in the survival time of patients, it gives a misleading picture of the benefit

of treatmentSlide25

Selection Bias

Choosing data that distorts the outcome of a test

May make a test look better or worse than it

really is,

in terms

of survivalSlide26

Over-Diagnosis Bias

Occurs when screening identifies an illness that would not have shown clinical signs before a person’s death from other causes

Makes screening efforts look good because of increased identification of abnormalities

Individual may undergo unnecessary treatment, with its accompanying riskSlide27

Avoiding Bias

Randomized

controlled trial

Through

randomization, different prognostic factors are

balanced between

groups, and the “true” screening or treatment effect can be determined Slide28

Outcomes Research

A relatively new field that seeks to understand the end results of clinical practices and interventions

Combines information about the care people are getting

Important in developing better ways to monitor and improve clinical careSlide29

Conclusion

Clinical

epidemiology

Involves

the application of epidemiologic methods to improve the quality and value of patient care

Involves assessment of the efficacy of screening, diagnosis, and treatment strategies in

clinical settings