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Critical Appraisal of Research Articles: Therapy

Screening

  • Why was the study done (what was the research question)?
  • Was the study design appropriate?
  • Are there potential conflict of interest issues?

Definitions

Number needed to treat (NNT) - The number of patients who need to be treated with the specified intervention to prevent one bad outcome or produce one good outcome over the period of time specified in the study.

Experimental event rate (EER) - The proportion of patients in the experimental treatment group who are observed to experience the outcome of interest.

Control event rate (CER) - The proportion of patients in the control group who are observed to experience the outcome of interest.

Absolute risk reduction (ARR) - The absolute arithmetic difference in rates of bad outcomes between experimental and control participants in a trial.

Relative risk reduction (RRR) - The proportional reduction in rates of bad outcomes between experimental and control participants in a trial.

Confidence Interval (CI) - A measure of the precision of the results of a study

P value - Refers to the probability that any particular outcome would have arisen by chance. The smaller the P value the less likely the data was by chance and more likely due to the intervention. Standard scientific practice, usually deems a P value of less than 1 in 20 (expressed as P=.05) as "statistically significant". The smaller the P value the higher the significance.

Therapy Article: Critical Appraisal

Validity           

              

 Questions to ask                          

Patient Follow-up

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

Was follow-up complete?

 
  • Is there outcome data for all patients who entered the trial?
  • Was the percentage of patients without outcome datab similar between groups?
  • Were reasons why patients dropped out or were missing outcome data well-described?

Randomization

Was the allocation (assignment) of patients to treatment randomized?

Was the allocation concealed?

 

  • Were patients selected at random from the target population?
  • Was the assignment randomized?
  • Was the method to generate randomization appropriate?
  • Was evidence of concealment provided?

Intention to Treat Analysis

Were patients analyzed in the groups to which they were randomized?

Were all randomized patient data analyzed?

 

  • Were all patients analyzed in the groups to which they were randomized?
  • What percentage of patients was excluded from the analyses?
  • How were missing outcomes handled?

 

Similar Baseline Characteristics of Patients

Were groups similar at the start of the trial?

 

  • Potential groups needing blinding: patients, providers, raters or assessors, data analysts
  • If appropriate, was the integrity of the blinding tested and found to have been preserved?

Equal Treatment

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

 

  • Were patients in the different groups treated differently in any way (other than the intervention)?

 

 

Summary of the article's validity

 

 

Notable strengths:

Weaknesses or concerns:

How serious are the threats to validity and in what direction could they bias the study outcomes?

Calculations

Estimating the size of the treatment effect

  Outcome
Yes		 Outcome
No
Treated (Y) a b
Control (X) c d

Risk of Outcome: Y = a/(a+b)
Risk of Outcome: X = c/(c+d)

  • Relative Risk (RR) is the risk of the outcome in the treated group (Y) compared to the risk in the control group. RR = Y/X
  • Relative Risk Reduction (RRR) is the percent reduction in risk in the treated group (Y) compared to the control group (X). RRR = 1-RR x 100%

  • Absolute Risk Reduction (ARR) is the difference in risk between the control group (X) and the treatment group (Y). ARR = X-Y

  • Number Needed to Treat (NNT) is the number of patients that must be treated over a given period of time to prevent one adverse outcome. NNT = 1/ARR

Subject Guide

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Tom Harrod
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