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 ROFECOXIB AND NAPROXEN IN PATIENTS WITH RHEUMATOID ARTHRITIS
Bombardier C, et al. N Engl J Med 2000;343:
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 Rofecoxib Naproxen Outcome N total N with Event GI
4047 56
4029
121 MI 17 4
Bombardier C, et al. N Engl J Med 2000;343:
Curfman G, et al. N Engl J Med 2005;353:

7. Incidence rate

8. Calculating incidence rate
Rofecoxib
Naproxen
Outcome
N total
N with Event
Person-years at risk GI
4047 56
2667
4029
121
2689 MI 17
2315 4
2316
Bombardier C, et al. N Engl J Med 2000;343:
Curfman G, et al. N Engl J Med 2005;353:

9. Prevalence

10. Prevalence Characteristic Rofecoxib group Naproxen group Age, years
58±9
58±10
Female sex
79.6%
79.8%
Etc…

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
Rofecoxib
Naproxen
Outcome
Absolute Risk (AR)
Incidence Rate (IR)
Relative Risk
Incidence Rate Ratio GI
1.4%
2.1
3.0%
4.5
0.47 MI
0.42%
7.3
0.10%
1.7
4.20
4.29

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
Rofecoxib
Naproxen
Outcome
Absolute Risk (AR)
Incidence Rate (IR)
Absolute Risk Difference
Incidence Rate Difference GI
1.4%
2.1
3.0%
4.5
-1.6
-2.4 MI
0.42%
7.3
0.10%
1.7
0.32
5.6
Time endpoint is 60 minutes

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 / ( ) = 62.5; on average, 63 patients would need to receive rofecoxib, as opposed to naproxen, to prevent one additional GI event
NNH = 1 / ( ) = 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:

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:

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
GI event MI
Yes No
Group
Rofecoxib
56 (a)
3991 (b)
17 (a)
4030 (b)
Naproxen
121 (c)
3908 (d)
4 (c)
4025 (d)

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