Worksheet for Using an Article

About
Therapy or Prevention

Citation:

______________________________________________________________________________

Guide

Comments

I. Are the Results of the Study Valid?

1. Was the assignment of patients to treatment randomized?

·  Was allocation to treatment and control groups randomized? ·  How was randomization carried out? ·  Was it concealed?

[ ] Yes            

[ ] No            

[ ] Can't Tell

2. Were all patients who entered the trial properly accounted for and attributed at its conclusion?

1.Was follow-up complete? - > 80 % of subjects completed the study - duration of study sufficient 2.Were patients analyzed in the groups to which they were randomized (intention to treat analysis)?

[ ] Yes            

[ ] No            

[ ] Can't Tell

3. Were patients, their clinicians, and study personnel 'blind' to treatment?

·  Single, double or triple blind ? ·  How was it done? ·  Could there have been unblinding during the study (e.g. adverse effects of Rx) ?

[ ] Yes            

[ ] No            

[ ] Can't Tell

4. Were the groups similar at the start of the trial?

·  Baseline prognostic factors (demographics, co-morbidity, disease severity, other known confounders) balanced? ·  If different, were these adjusted for?

[ ] Yes            

[ ] No            

[ ] Can't Tell

5. Aside from the experimental intervention, were the groups treated equally?

·  Co-intervention? ·  Contamination? ·  Compliance?

[ ] Yes            

[ ] No            

[ ] Can't Tell

6. Overall, are the results of the study valid?

[ ] Yes            

[ ] No            

[ ] Can't Tell

II.  What are the Results?

1. How large was the treatment effect?	·  Absolute risk reduction? ·  Relative risk reduction?
2.How precise was the estimate of the treatment effect?	·  Confidence intervals?
	Relative risk reduction (RRR)	Absolute risk reduction (ARR)	Number needed to treat (NNT)
CER	EER	CER – EER CER	CER-EER	1/ARR
	95% CI Þ

III.             Will the results Help Me in Caring for My Patients?

1. Can the results be applied to my patient  care?

·  Patients similar for demographics, severity, co-morbidity and other prognostic factors? ·  Compelling reason why the results should not be applied?

[ ] Yes            

[ ] No            

[ ] Can't Tell

2. Were all clinically important outcomes considered?

·  Are substitute endpoints valid?

[ ] Yes            

[ ] No            

[ ] Can't Tell

3. Are the likely treatment benefits worth the potential harms and costs?

·  NNT for different outcomes?

[ ] Yes            

[ ] No            

[ ] Can't Tell

Method I: f	Risk of the outcome in your patient, relative to patients in the trial. Expressed as a decimal: _____ ,   NNT/f = ______ / ______ = ______ (NNT for patients like yours)
Method II:	Your patient’s expected event rate if they received the control treatment (PEER) =_____ 1/(PEER x RRR)= 1/________ = ______  (NNT for patients like yours)

Statistics for interpreting the importance and precision of therapeutic results

	Yes	No
Exposed	a	b
Not Exposed	c	d

Control event rate (CER) = c/c+d

Experimental event rate (EER) = a/a+b

(a) Relative Risk (RR) = EER/CER=(a/a+b)/(c/c+d)

(b) Relative Risk Reduction (RRR) = CER-EER/CER
(commonest reported measure of dichotomous treatment effect)

(c) Absolute Risk Reduction (ARR) = CER-EER

(d) Number Needed to Treat (NNT) = 1/ARR
A certain risk reduction may appear impressive but how many patients would you have to treat before seeing a benefit? This concept is called "number need to treat" and is one of the most intuitive statistics for clinical practice.

For example if

	Yes	No
Exposed	8	992
Not Exposed	10	990

The RR = (8/1000) / (10/1000) = 0.8 making the RRR = (1-0.8/1)=0.2 or 20%. Although this sounds impressive, the absolute risk reduction is only 0.01-0.008=.002 or 0.2%. Thus the NNT is 1/0.002=500 patients. It is obvious that on an individual patient basis the pre-intervention risk or probability is a major determinant of the degree of possible post-intervention benefit, yield, or risk reduction.

Confidence Interval

The estimate of where the true value of a result lies is usually expressed in terms of a 95% confidence interval (CI), or confidence limits. These define the range that includes the true relative risk reduction 95% of the time. If confidence limits are not provided you can calculate them if you have been given standard error of the RRR or relative risk. Just multiply the standard error by 2: the plus and minus values of this are the upper and lower values for the confidence interval.

Alternately the 95% confidence interval for an ARR can be calculated by:

=+/-1.96 ?[CER X (1-CER)/# control patients + EER X (1-EER)/# experimental patients]               The CI for the NNT is just 1/limits of CI for ARR.