PROGNOSIS ebm.pptx

7/28/2019 PROGNOSIS ebm.pptx

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Dewi Masyithah Darlan

Medical Faculty of USU

PROGNOSIS

Evidence Based Medicine


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Introduction - Prognosis

Important phase of a disease -

progression of a disease

Prognosis : the prediction of the future

course of events following the onset ofdisease.

can include death, complications,

remission/ recurrence, morbidity,disability, and social or occupational

function


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Introduction PrognosisNatural History Studies

Natural history studies permit the

development of rational strategies for: early detection of disease

e.g. Invasive cervical CA

treatment of diseasee.g. Ptyriasis versicolor


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PrognosisPatients at riskof target event

Prognosticfactor

Time

Suffer target

outcome

Do not suffer

target outcome

?

?


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Introduction PrognosisNatural History Studies

Natural history studies permit the

development of rational strategies for: early detection of disease

e.g. Invasive cervical CA

treatment of diseasee.g. Ptyriasis versicolor


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A. Are the results of this

prognosis study valid?


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A.1. Was a defined, representative sample

of patients assembled at a common

(usually early) point in the course of theirdisease?

How well define the individuals in thestudy criteria representative of the

underlying population:

inclusion, exclusion

sampling method

Similar: well-defined point in the course

of their disease -- cohort


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A1. Was a defined, representative sample

of patients assembled at a common

(usually early) point in the course of theirdisease?

A prognostic study is biased if it yields a

systematic overestimate or underestimate of thelikelihood of adverse outcomes in the patients

under study

When a sample is systematically different from

the population of interest and is therefore likely

biased because patients will have a better or

worse prognosis than those in the population of

interest -

unrepresentative


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A2. Was follow-up sufficiently long and

complete?

Ideal follow-up period

until every patient recovers or has one

the other outcomes of interest until the elapsed time of observation is

of clinical interest to clinicians or

patients Short follow up time:

Too few study patients with outcome of interest

- little information of use to a patient


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A2. Was follow-up sufficiently long and

complete?

Loss to follow up - influence the

estimate of the risk of the outcome -

validity?? patients are too ill (or too well)

Die

change address etc.

Most evidence journals require at least 80%follow-up for a prognosis study to be considered

valid


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Bias in Follow-up Studies

Assembly or susceptibility bias:when exposed and non-exposed groups

differ other than by the prognostics

factors under study, and the extraneousfactors affects the outcome of the study.

examples:

o differences in starting point of disease

(survival cohort)

o differences in stage or extent of disease,

prior treatment, age, gender, or race


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Bias in Follow-up Studies

Migration bias:o patients in one cohort leave their

original cohort, either moving to one of

the other cohorts under study ordropping out of the study altogether

Generalizability bias

o related to the selective referral of

patients to tertiary (academic) medical

centers


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A3.Were objective outcome criteria

applied a blind fashion?

investigators making judgments

about clinical outcomes are kept

blind to subjects clinicalcharacteristics and prognostic

factors.

Minimize measurement bias!


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A3.Were objective outcome criteria

applied a blind fashion?

Measurement bias can be minimized by: ensuring observers are blinded to the

exposure status of the patients using careful criteria (definitions) for

all outcome events

apply equally rigorous efforts toascertain all events in both exposure

groups


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A4. If subgroups with different prognoses

are identified, was there adjustment for

important prognostic factors?

Prognostic factors: factors associated with a

particular outcome among disease subjects. Canpredict good or bad outcome.

prognostic factors need not be causal, and in

fact they are often, but they must be strongly

associated with development of an outcome topredict its occurrence.

Examples:

age, tumor stage


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A4. If subgroups with different prognoses are

identified, was there adjustment for important

prognostic factors?

Risk factors:

o distinct from prognostic factorso include lifestyle behaviors and environmental

exposures that area assoc. with the

development of a target disorder

o Ex: smoking: important risk factors fordeveloping lung cancer, but tumor stage is the

most important prognostic in individuals who

have lung cancer.


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A5. Was there validation in an independent

group ("test-set") of patients?

Too see if this was done, wed look

for a statement in the studys

methods section describing a pre-

study intention to examine this

specific group of prognostic factors,

based on their appearance in a

training set or previous study.


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B. Are the results of this study

important?


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B1. How likely are the outcomes over time?

typically, results from prognosis studiesare reported in one of three ways: as a percentage of survival at a particular

point in time (such as 1 year or 5 year survivalrates)

median survival (the length of follow up by

which)

survival curves that depict, at each point intime

The result presentation: Kaplan-Meier curves


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Survival Rate

1 year survival

A. Good

B. 20%

C. 20%

D. 20%

Median survival

A. ?

B. 3 months

C. 9 months

D. 7.5 months


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B2. How precise are the prognostic estimates?

Precision - 95% confidence intervalThe narrower the confidence interval,

the more precise is the estimate.

If survival over time is the outcome ofinterest - earlier follow-up periods

usually include results from more patients

than in later periods, so that survivalcurves are more precise in the earlier

periods


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C. Can we apply this valid,

important evidence aboutprognosis to our patient?


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C1. Are the study patients so different

from ours that we should not use the

results at all in making predictions for ourpatients?

for more differences, the answer tothis questions is no and thus we can

use the study results to inform our

prognostic conclusions


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C2. Will this evidence make a clinically

important impact on our conclusions about

what to offer or tell our patient?Useful for: initiating or not therapy

monitoring therapy that has been initiated

deciding which diagnostic tests to order

providing patients and families with the

information they want about what the future

is likely to hold for them and their illness. Communicating to patients their likely fate

Guiding treatments decisions

Comparing outcomes to make inferences about

quality of care


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