Critical appraisal of Prognostic studies
Are the results of the study valid? (Internal Validity)
1.Was the defined representative sample of patients assembled at a common(usually early) point in the course of their disease)?
What is best?
It is preferable if study patients are enrolled ata uniformly early time in the disease usuallywhen disease first becomes manifest. Suchgroups of patients are called an ‘inception
cohort’. Patients should also be representativeof the underlying population. Patients fromtertiary referral centres may have moreadvanced disease and poorer prognoses thanpatients form primary care.
This paper: Yes No 

Where do I find the information?
The Methods section should describe the stage
at which patients entered the study (e.g., at thetime of first myocardial infarction; Stage 3 breastcancer). The Methods section should also
provide information about patient recruitment,
whether patients were recruited from primarycare or tertiary referral centres.

Unclear Comment:

2. Was patient follow-up sufficiently long and complete?
What is best?
Length of follow-up should be long enough todetect the outcome of interest. This will varydepending on the outcome (e.g., for pregnancy
outcomes, nine months; for cancer, manyyears). All patients should be followed from thebeginning of the study until the outcome ofinterest or death occurs. Reasons for nonfollow-up should be provided along withcomparison of the demographic and clinicalcharacteristics of the patients who wereunavailable and those in whom follow-up wascomplete.
This paper: Yes  No  Unclear 

Where do I find the information?
The Results section should state the median ormean length of follow-up.
The Results section should also provide thenumber of and the reasons for patients being
unavailable for follow-up. A comparison of thetwo groups (those available and thoseunavailable) may be presented in table form or
the authors may simply state in the text whether
or not there were differences.

Comment:

3. Were outcome criteria either objective or applied in a ‘blind’ fashion?
What is best?
A clear definition of all outcomes should beprovided. It is ideal if less objective outcomesare assessed blindly, that is, the individual
determining the outcome does not knowwhether the patient has a potential prognostic
factor.
This paper: Yes No 

Where do I find the information?
The Methods section should provide a clear
definition or explicit criteria for each outcome
and whether determination is blinded toprognostic factors will be found in either theMethods or Results sections.

Unclear 

Comment:
4. If subgroups with different prognoses are identified, did adjustment for important prognostic
factors take place?
What is best?
A prognostic factor is a patient characteristic(e.g., age, stage of disease) that predicts thepatient’s eventual outcome. The study shouldadjust for known prognostic factors in theanalysis so that results are not distorted.

Where do I find the information?
The Results section should identify any
prognostic factors and whether or not thesehave been adjusted for in the analysis. Also lookat the tables and figures for evidence of this(e.g., there may be separate survival curves forpatients at different stages of disease or fordifferent age groups).

Centre for Evidence-Based Medicine, University of Oxford, 2010
This paper: Yes No Unclear 

Comment:

What are the results?
How likely are the outcomes over time?
There are several different ways of reporting outcomes of disease. Often they are reported simply
as a rate (e.g., the proportion of people experiencing an event). Expressing prognosis as a rate
has some advantages. It is simple, easily communicated and understood and readily committed tomemory. Unfortunately, rates convey very little information and there can be important differencesin prognosis within similar summary rates. For this reason survival curve are used to estimatesurvival of a cohort over time. It is a useful method for describing any dichotomous outcome (notjust survival) that occurs only once during the follow-up period, The figure below shows thesurvival curves for three diseases with the same survival rate at 5 years. Notice that the summary
rate obscures important differences to patients

Figure. Five year curves for three different diseases.
How precise are the prognostic estimates?
To determine the precision of the estimates we need to look at the 95% confidence intervals (CI)around the estimate. The narrower the CI, the more useful the estimate. The precision of theestimates depends on the number of observations on which the estimate is based. Since earlier
follow-up periods usually include results from more patients than later periods, estimates on theleft hand side of the curve are usually more precise. Observations on the right or tail end of thecurve are usually based on a very small number of people because of deaths, dropouts and lateentrants to the study. Consequently, estimates of survival at the end of the follow-up period arerelatively imprecise and can be affected by what happens to only a few people.

Can I apply this valid, important evidence about prognosis to my patient?

The questions that you should ask before you decide to apply the results of the study to yourpatients are:

Is my patient so different to those in the study that the results cannot apply?

Will this evidence make a clinically important impact on my conclusions about what tooffer to tell my patients

Centre for Evidence-Based Medicine, University of Oxford, 2010

Centre for Evidence-Based Medicine, University of Oxford, 2010

Centre for Evidence-Based Medicine, University of Oxford, 2010