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Which Treatment ?

Explore different treatments and their efficacy in reducing stroke risk for a 64-year-old male patient with atrial fibrillation. Learn the impact of economic reforms on unemployment rates and understand the concept of risk reduction. Find out the importance of confidence intervals in medical research.

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Which Treatment ?

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  1. Which Treatment ? • For a patient, 64-year-old male • No HT, DM, Heart failure, LV dysfunction • Having non-rheumatic atrial fibrillation • Treatment ‘A’ reduces annual stroke risk by 40% • Treatment ‘B’ requires 250 patients to be treated for one year to prevent one stroke • Treatment ‘C’ reduces annual stroke risk from 1.0% to 0.6%

  2. Newspaper headlines: Economic reforms succeed • Economic reforms led to decline in unemployment from 20% to 15%, thus reducing it by 25%

  3. Newspaper headlines: Economic reforms succeed • Economic reforms led to decline in unemployment from 20% to 15%, thus reducing it by 25%. • How? Difference is only 5%. • If 20% = 100% • Then 15% = 75% • And 5% = 25%

  4. Absolute risk reduction Baseline risk Relative risk Relative risk reduction Different ways of expressing effects • Economic reforms led to decline in unemployment rate from 20% to 15%, thus reducing it by 25% • 20% - 15% = 5% • If 20% = 100% • Then 15% = 75% • And 5% = 25%

  5. In an Intervention trial • Intervention led to decline in risk (incidence) of mortality from 20% (in control group) to 15% (in intervention group), thus reducing it by 25%. • Risk Difference is the simple difference between the two risks = 5%. • If 20% is taken as 100%, then • 15=75% = RR (15%/20%=0.75=75%) • And 5% = 25% i.e. RRR (100-75 i.e. 100-RR (%) or in decimals, 1 - RR

  6. What does risk difference of 5% mean? • 5 per cent = 5 per 100, • 5 less death per 100 need to be treated with new t/t • To have one less death, how many need to be treated? • What if Risk difference is 10%; 20%; 50% • NNT = 100/RD (%); in decimals 1/RD

  7. A True Story • Husband and pregnant wife meet their doctor • Husband asks : When is the delivery expected doctor? • Doctor : What’s the LMP • Wife : 1st March 2009 • Doctor : EDD is 8th December 2009 • Husband : OK, I will be here on 7th Dec. 2009 • Doctor : Oh sorry, the delivery may be earlier or later than 7th Dec. • And so on

  8. Degree of desired confidence level determines the width of the range (Interval)

  9. Similarities b/w EDD range and C.I. • Both need data and calculation • Both capture the margin of error • Both indicate range of possibilities • Width of the range is directly related to the desired level of certainty • This is only one point of true or right value in both

  10. Differences b/w EDD range & C.I. • EDD predicts about individual whereas C.I. about population • No definite formula for EDD but for every C.I. there is definite formula • Formula for C.I. differs depending on the type of data (no such for EDD) • Width of C.I. inversely related to sample size (? In EDD)

  11. Newspaper headlines • Barack Obama’s popularity rating is 55% (error +/- 10%) • How to reduce the error? • Bigger the sample size, less the error; and narrower is the width of CI • How much width of CI is acceptable? • 45% (error +/- 10%) • 65% +/- 10%

  12. Two more concepts • Width of CI at a level (say 95%) depends on the sample size • Bigger the sample size, narrower the CI • A good width of CI is the one which yields the same answer at both its ends (limits)

  13. What is 95% confidence interval? • 95% confident that the true effect is within the range • A point in the centre is the finding from the study subjects • Lines on either side denote the margin of error (range of values consistent with the data)

  14. Interventions Q vs Placebo Study D (N=4000) (-0.1% to - 2%) Interventions P vs Placebo Study Q (N=400) (-1% to - 19%) -50 -40 -30 -20 -10 0 10 20 30 40 50 Risk difference 95% C.I. For two studies with small (C) and Large (D) sample size. p values approx 0.03 for both studies

  15. Interventions Y vs Placebo Study B (N=10,000) (-0.1% to + 0.1%) Study A (N=20) Interventions X vs Placebo (-48% to + 48%) -50 -40 -30 -20 -10 0 10 20 30 40 50 Risk difference 95% C.I. For two studies with small (A) and Large (B) sample size. p values 1.0 for both studies

  16. THANK YOU

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