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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THE
END
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