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Analyzing Randomized Control Trial: ITT vs. PP vs. AT Proceedings from Journal club…..

Analyzing Randomized Control Trial: ITT vs. PP vs. AT Proceedings from Journal club…. Vikash. Basic Analysis of RCT:. To calculate: Relative Risk (RR) Relative Risk Ratio (RRR) Attributable Risk (AR) Absolute Risk Reduction (ARR) Number Needed to treat (NNT)

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Analyzing Randomized Control Trial: ITT vs. PP vs. AT Proceedings from Journal club…..

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  1. Analyzing Randomized Control Trial: ITT vs. PP vs. ATProceedings from Journal club….. Vikash

  2. Basic Analysis of RCT: • To calculate: • Relative Risk (RR) • Relative Risk Ratio (RRR) • Attributable Risk (AR) • Absolute Risk Reduction (ARR) • Number Needed to treat (NNT) • For Time dependant analysis • Survival Analysis by Kaplan- Mier or by Cox Proportional Model. • Then, Apply test of Significance.

  3. For Dichotomous Outcome: • RR = ID (Exposed)/ ID (Unexposed) = a/a +b / c /c +D • RRR = 1 – RR • ARR = ID (Unexposed) - ID (Exposed)

  4. Attributable Risk = (OR – 1) PE / 1+ [ (OR-1) PE] x 100 • Where OR = Odds Ratio = ad / bc • Number Needed to treat (NNT) = 1/ARR • RR = 0. 4 /0.5 = 0.8 • RRR = 0.2 • ARR = 0.2 – 0.25 = - 0.05 • NNT = 1/ARR = 20

  5. Intention to treat Analysis • Also called As randomized or Method Effectiveness analysis. • Compare outcome according to the randomized group (Gold Standard). • Adherence to intervention not necessary. Advantages: • Randomization is maintained: • Treatment assignment is based on chance alone. • Randomization provides Theoretical foundation for Statistical test of significance. Disadvantages: • Doesn’t take into account Protocol violation.

  6. Group may not be comparable at the end. • Not adhering to treatment or vice versa. • Eligibility for the trial was incorrect. • Loss to follow up. • Estimates of non – complied in the efficacy dilutes difference between groups. • Analysis may underestimate adverse effect. Why gold standard ? • Randomization is maintained • Difficulty in defining compliance. • Effect in complied group may be due to factor of compliance.

  7. Per Protocol Analysis: • Analyze only those who fully complied to protocol. • Doesn’t included cross- over in final analysis. • Provides fair idea of efficacy for treatment. • May be Biased (randomization compromised) As treated Analysis: • Subject analyzed according to treatment taken or not. (no relation with randomization). • Non compliant from treatment and vice versa analyzed accordingly. • AT is shown if ITT shows no effect ( why trial done).

  8. Hypothetical Example: RCT to see the effect of Aspirin in incidence of Myocardial Re-infarction in patient with h/o MI. • ARR by ITT = 20.833% - 16.66% = 4.17% • ARR by PP = 23% - 16.66% = 6.34% • ARR by AT = 21.25% - 16.25% = 5%

  9. References: • Redmond C, Armitage P editors. Biostatics in Clinical Trials. 1st ed. Sussex. John Wiley & Sons ltd. 2001. p243- 6. • Haynes RB, Sacket DL, Guyat GH, Tugwell P. Clinical Epidemiology. 3rd ed. Baltimore. Lippincott Williams & Wilkins.2006. p 95 & 116. • Fletcher RW, Fletcher SW. Clinical Epidemiology: the essential. 4th ed. Baltimore. Lippincott Williams & Wilkins. 2005. p 136-9.

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