ASPIRE CLASS 6: Interpreting Results and Writing an Abstract

1. ASPIRE CLASS 6: Interpreting Results and Writing an Abstract • Jordan King, PharmD, MS

2. Interpreting Results • Explain the difference between cumulative incidence, incidence rate, and prevalence • Explain the difference between relative risk, odds ratio, and hazard ratio • Calculate the number needed to treat and the number needed to harm

3. COMPARISON OF UPPER GASTROINTESTINAL TOXICITY OF ROFECOXIBAND NAPROXEN IN PATIENTS WITH RHEUMATOID ARTHRITIS • Bombardier C, et al. N Engl J Med 2000;343:1520-8. • Design: Randomized, double-blind, active-control • Intervention: 50 mg of rofecoxib daily vs 500 mg of naproxen twice daily • Primary Outcomes: • Efficacy – confirmed clinical upper gastrointestinal events (gastroduodenal perforation or obstruction, upper gastrointestinal bleeding, and symptomatic gastroduodenal ulcers) • Safety – mortality, ischemic cerebrovascular events, myocardial infarctions

4. Measures of disease frequency (measures the occurrence of illness) • Incidence (occurrence of disease) • Rate or proportion • Prevalence (disease status) Measures of association (comparisons between two or more interventions) • Relative (ratio) • Absolute (difference)

5. Incidence proportion (risk)

6. Calculating risk Bombardier C, et al. N Engl J Med 2000;343:1520-8. Curfman G, et al. N Engl J Med 2005;353:2813-4.

7. Incidence rate

8. Calculating incidence rate Bombardier C, et al. N Engl J Med 2000;343:1520-8. Curfman G, et al. N Engl J Med 2005;353:2813-4.

9. Prevalence

10. Prevalence

11. Measures of association • Used to help us determine differences in effect between exposures • Calculated from the measures of disease frequency • Can be absolute or relative • Absolute = difference (subtract) • Relative = ratio (divide)

12. Relative Measures • Ratio of risk or rates • Calculated as RR = Risk1/Risk2 • Interpretation: relative effect = RR – 1 • RR = 1.4%/3.0% = 0.47 • Relative effect = 1 – 0.47 = 0.53; there is a 53% relative reduction in the risk of a GI event in the rofecoxib group compared to the naproxen group • Null = 1

13. Absolute Measures • The difference in the risk (probability of event) or rate between two groups • Calculated as Risk1 – Risk2 • Interpretation: • ARD = 1.4% - 3.0% = -1.6% there is a 1.6% absolute reduction in the risk of a GI event in the rofecoxib group compared to the naproxen group • Null = 0

14. Number Needed to Treat (NNT) &Number Needed to Harm (NNH) • The average number of patients who need to be treated to prevent (or cause) one additional event • Calculated from absolute differences • 1/ARD • Interpretation: • NNT = 1 / (0.014 - 0.030) = 62.5; on average, 63 patients would need to receive rofecoxib, as opposed to naproxen, to prevent one additional GI event • NNH = 1 / (0.0042 - 0.0010) = 312.5; on average, 313 patients would need to receive rofecoxib, as opposed to naproxen, to cause one additional MI • TIME!

15. Interpreting and presenting the results(Efficacy) • From the abstract: “During a median follow-up of 9.0 months, 2.1 confirmed gastrointestinal events per 100 patient-years occurred with rofecoxib, as compared with 4.5 per 100 patient-years with naproxen (relative risk, 0.5; 95 percent confidence interval, 0.3 to 0.6; P<0.001).” • What was the measure of disease frequency? • What was the measure of association? • What was the reference group? • How do we interpret these values? Bombardier C, et al. N Engl J Med 2000;343:1520-8.

16. Interpreting and presenting the results (Safety) • From the abstract: “The incidence of myocardial infarction was lower among patients in the naproxen group than among those in the rofecoxib group (0.1 percent vs. 0.4 percent; relative risk, 0.2; 95 percent confidence interval, 0.1 to 0.7)” • What was the measure of disease frequency? • What was the measure of association? • What was the reference group? • How do we interpret these values? Bombardier C, et al. N Engl J Med 2000;343:1520-8.

17. Other measures of effect • Hazard ratio (HR) • Used for time to event analysis • Calculated from a Cox Proportional Hazards model • Commonly combined with Kaplan-Meier curves and statistics • Ratio of hazard rates (relative measure) • Hazard h(t) is different than Survival S(t) • You don’t need to worry about this • How often a particular event happens in one group compared to how often it happens in another group, over time • Null = 1

18. Other measures of effect

19. Calculating Odds Ratios

20. Writing an Abstract • List the essential elements of an abstract • Recognize and apply succinct writing to an abstract

21. Tips for writing a conference abstract • Start with the conference writing guide! • Provide only main objectives, methods, results, and conclusions • Space is very limited (you can use abbreviations to save characters, but limit number) • Do not list results that are not stated in the methods • Statistics used is optional - I typically describe statistic used to assess primary outcome (e.g., Cox proportional hazards models were used to ….) • Give just enough information in the abstract to make the reviewers interested in hearing more • A reviewer will be unable to evaluate the quality of the research from an abstract alone • Flow is very important • Abstract must be stand alone

22. Other thoughts • Think about best audience when choosing where to submit • Conference • Poster session within conference • Key words are sometimes made up by you and sometimes chosen from a list provided by the conference • Acceptance rates vary greatly between conferences • Don’t worry about a rejection • Consider timing of manuscript submission and embargo policies • Very rare to submit an abstract with results pending now that you are not a student (most conferences will not accept and I don’t recommend) • Posters last a minute, manuscripts are forever