Prognosis II Flashcards
prognostic factors
general term that describes characteristics predictive of any type of future outcome is a prognostic factor
risk factors
predictors of future adverse events usually are referred to as risk factors
target disorder/diease not developed. influence development of target disorder/disease
risk factor– we dont have illness yet ex smoking to lead to cancer
prognosis– have illness
challenge of prognosis- 3
THE OUTCOME that are possible
THE LIKELIHOOD that the outcome will occur
THE TIME FRAME
prognosis factor- 3 evidence based principles
evidence about the accuracy of the prognostic factor valid (quality assessment)?
does the prognostic factor generate important info about patient outcome (probability and magnitude considerations)?
can I apply the prognostic factor to a specific patient (clinical use)?
quality assessment-evidence about prognostic factor valid? 4 questions
- well defined sample of patients? -inception cohort
- acceptable follow up rates? -complete and long enough to capture the outcome of interest
- utilize objective outcome criteria? -blind fashion
- subgroups appropriately considered?
Prognosis important? 3
evidence about the prognostic factor
- probability of outcomes
- magnitude of association with factor
- precision of estimates
Prognosis statistical analysis- linear regression
linear regression:
prognostic factor- cont (0-100 scale), categorical (pos or neg)
outcome-continuous (0-100 scale)
linear regression prognostic factors
crude= one considered at a time (univariate or simple regression)
adjusted= all considered at same time (multivariate or multiple regression)
r2-estimate of total variance explained
prognosis regression quantities
outcome (dep variable)- total variance (ex R square) explained in outcome
prognostic factors (indep variable)- relative contribution compared to another (standardized coefficients) and absolute contribution to prediction equation (unstandardized coefficients)
prognosis statistical analysis-logistic regression
prognostic factors- continuous (0-100 scale), categorical (pos or neg)
outcome-categorical (pos or neg)
Prognosis estimate- relative risk (RR)
the gold standard
cohort study design (prospective), exposure status is known, all subjects followed forward, outcome status is measured at later time, comparing probabilities
time consuming, expensive, and gold standard for cohort
RR= (A/A=B)/ (C/C+D)
incidence of outcome in exposed divided by the incidence of outcome in non exposed
Interpretation of RR
RR- starts with prognostic factor (exposure), follows forward outcome, comparing probabilityof events
therefore, RR estimates probability of disease given presence of prognostic factor
Interpretation of RR statistic
if RR > 1.0 increased probability of outcome among those with prognostic factor (exposed subjects)
if RR < 1.0 decreased probability of outcome among those exposed with prognostic factor (exposed subjects)
if RR= 1.0 probability of outcome is similar among all subjects
Odds ratio
odds of exposure among individuals with outcome divided by the odds of exposure among individuals without outcome
OR= (AxD)/(BxC)
prognosis estimate-OR
the “alternative”
doesn’t have to be a prospective study-
classic design-case sontrol (retrospective) subjects with and without disease are enrolled
compare the odds of disease in the two groups
