The Role of the Statistician in Clinical Research Teams

1. The Role of the Statistician in Clinical Research Teams Elizabeth Garrett-Mayer, Ph.D. Division of Biostatistics Department of Oncology

2. Statistics • Statistics is the art/science of summarizing data. • Better yet … summarizing data so that non-statisticians can understand it. • Clinical investigations usually involve collecting a lot of data. • But, at the end of your trial, what you really want is a “punchline”: • Did the new treatment work? • Are the two groups being compared similar or different? • Is the new method more precise than the old method? • Statistical inference is the answer!

3. Do you need a statistician as part of your clinical research team? • YES! • Simplest reasons: s/he will help optimize • Design • Analysis • Interpretation of results • Conclusions

4. What if I already know how to calculate sample size and perform a t-test? • Statisticians might know of a better approach • Trained more formally in design options • More “bang for your buck” • Tend to be less biased • Adds credibility to your application • Use resources that are available to you

5. Different Roles • Very collaborative • Active co-investigator • Helps develop aims and design • Brought in at an early stage in planning • Contributes input throughout trial planning and ongoing study • Consultants • Inactive co-investigator • Often not brought in until either • you need a sample size calculation several days before submission • trial has been criticized/rejected for lack of statistical input • you’ve finally collected all of the data and don’t know what to do next. • Seldom involved in planning or analysis.

6. Find a statistician early • Your trial can only benefit from inclusion of a statistician • Statisticians cannot correct a poorly designed trial after the trial has begun. • “Statistical adjustment” in analysis plan does not always work. • Ignorance is not bliss: • Some clinical investigators are trained in statistics • … but usually not all aspects! • Despite inclination to choose a particular design or analysis method, there might be better ways.

7. Example: Breast Cancer Prevention in Mice • NOT a clinical study (thank goodness!) • Mouse study, comparing 4 types of treatments • Her-2/neu Transgenic Mouse • Prevention: which treatment is associated with the longest tumor formation time? A intra-ductal B intra-ductal No treatment A intravenous

8. Example: Breast Cancer Prevention in Mice • Each oval represents a mouse and dots represent ducts • Lab researchers developed the design • Varying numbers of mice for each of the four treatment groups • Multiple dose levels, not explicitly shown here A intra-ductal B intra-ductal No treatment A intravenous

9. How to analyze? • Researchers had created their own survival curves. • Wanted “p-values” • Some design issues: • What is the unit of analysis? • How do we handle the imbalance? • Treatment B has no “control” side

10. Our approach • Statistical adjustments used • Treat “side of mouse” as unit of analysis • Cannot use mouse: multiple treatments per mouse in many cases. Too many categories (once dose was accounted for). • Cannot use duct: hard to model “dependence” within side and within mice. • Still need to include dependence within mice. • Need to adjust for treatment on “other side” • Problems due to imbalance of doses • Could only adjust for “active” versus “inactive” treatment on other side.

11. Our approach • We “saved” this study! • Not optimal, but “best” given the design • Adjustments might not be appropriate • We “modeled” the data—we made assumptions • We could not implement all the adjustments we would have liked to • Better approach? • Start with a good design! • We would have suggested balance • We would NOT have given multiple treatments within mice.

12. Statisticians: Specific responsibilities • Design • Choose most efficient design • Consider all aims of the study • Particular designs that might be useful • Cross-over • Pre-post • Factorial • Sample size considerations • Interim monitoring plan

13. Statisticians: Specific responsibilities • Assistance in endpoint selection • Subjective vs. objective • Measurement issues • Should any measurement error be considered? • What if you are measuring pain? QOL? • Multiple endpoints (e.g. safety AND efficacy) • Patient benefit vs. biological/PK endpoint • Primary vs. secondary • Continuous vs. categorical outcomes

14. Statisticians: Specific responsibilities • Analysis Plan • Statistical method for EACH aim • Account for type I and type II errors • Stratifications or adjustments are included if necessary • Simpler is often better • Loss to follow-up: missing data?

15. Sample size and power • The most common reason we are contacted • Sample size is contingent on design, analysis plan, and outcome • With the wrong sample size, you will either • not be able to make conclusions because the study is “underpowered” • waste time and money because the study is unnecessarily large • And, with wrong sample size, you might have problems interpreting your result: • Does the lack of a significant result show that the treatment does not work, or is it due to my sample size being too small? • Did the treatment REALLY work, or is the effect I saw too small to warrant further consideration of this treatment? • This is an issue of CLINICAL vs. STATISTICAL significance

16. Sample size and power • Sample size ALWAYS requires the investigator to make some assumptions: • How much better do you expect the experimental therapy group to perform compared to the standard therapy groups? • How much variability do we expect in measurements? • What would be a clinically relevant improvement? • The statistician CANNOT tell you what these numbers should be (unless you provide data) • It is the responsibility of the clinical investigator to define these parameters

17. Sample size and power • Review of power • Power = The probability of concluding that the new treatment is effective if it truly is effective • Type I error = The probability of concluding that the new treatment is effective if it truly is NOT effective • (Type I error = alpha level of the test) • (Type II error = 1 – power) • When your study is too small, it is hard to conclude that your treatment is effective

18. Example: sample size in multiple myeloma study • Phase II study in multiple myeloma patients (Borello) • Primary Aim: Assess clinical efficacy of activated marrow infiltrating lymphocytes (aMILs) + GM-CSF-based tumor vaccines in the autologous transplant setting for patients with multiple myeloma. • If the clinical response rate is ≤ 0.25, then the investigators are not interested in pursuing aMILs + vaccines further. • If the clinical response rate is ≥ 0.40, they would be interested in pursuing these further.

19. Example: sample size in multiple myeloma study • H0: p = 0.25 • H1: p = 0.40 • We want to know what sample size we need for a large power and small type I error. • If the treatment DOES work, then we want a high probability of concluding that H1 is “true.” • If the treatment DOES NOT work, then we want a low probability of concluding that H1 is “true.”

20. Sample size = 10; Power = 0.17 Distribution of H0: p = 0.25 Distribution of H1: p = 0.40 Probability distribution Proportion of responders Vertical line defines “rejection region”

21. Sample size = 30; Power = 0.48 Distribution of H0: p = 0.25 Distribution of H1: p = 0.40 Probability distribution Proportion of responders Vertical line defines “rejection region”

22. Sample size = 75; Power = 0.79 Distribution of H0: p = 0.25 Distribution of H1: p = 0.40 Probability distribution Proportion of responders Vertical line defines “rejection region”

23. Sample size = 120; Power = 0.92 Distribution of H0: p = 0.25 Distribution of H1: p = 0.40 Probability distribution Proportion of responders Vertical line defines “rejection region”

24. Not always so easy • More complex designs require more complex calculations • Usually also require more assumptions • Examples: • Longitudinal studies • Cross-over studies • Correlation of outcomes • Often, “simulations” are required for a sample size estimate.

25. Most common problems seen in study proposals when a statistician is not involved • Outcomes are not clearly defined • There is not an analysis plan for secondary aims of the study • Sample size calculation is too simplistic or absent • Assumptions of statistical methods are not appropriate

26. Examples: trials with additional statistical needs • Major clinical trials (e.g. Phase III studies) • Continual reassessment method (CRM) studies • Longitudinal studies • Study of natural history of disease/disorder • Studies with “non-random” missing data

27. Major trials • Major trials are usually monitored periodically for safety and ethical reasons. • Monitoring board: Data (Safety and) Monitoring Committee (DMC or DSMC) • In these trials you would ideally usethree statisticians (Pocock, 2004, Statistics in Medicine) • Study statistician • DMC statistician • Independent statistician • Why? • Interim analyses require “unbiased”analysis and interpretation of study data. • Industry- versus investigator-initiated trials … differences?

28. Study statistician • Overall statistical responsibility • Actively engaged in design, conduct, final analysis • Not involved in interim analyses • Should remain “blinded” until study is completed

29. DMC statistician • Experienced trialist • Evaluate interim results • Decide (along with rest of DMC) whether trial should continue • No conflict of interest

30. Independent Statistician • Performs interim analysis • Writes interim analysis report • No conflict of interest • Only person with full access to “unblinded” data until trial completion

31. High-maintenance trials • Some trials require statistical decision-making during the trial process • Simon’s “two-stage” design: • Stage 1: Treat about half the patients. • Stage 2: If efficacy at stage 1 meets a certain standard, the remainder of the patients are enrolled • “Adaptive” and “sequential” trials: final sample size is determined somewhere in the middle of the trial • Continual Reassessment Method …

32. Continual Reassessment Method • Phase I trial design • “Standard” Phase I trials (in oncology) use what is often called the ‘3+3’ design • Maximum tolerated dose (MTD) is considered the highest dose at which 1 or 0 out of six patients experiences DLT. • Doses need to be pre-specified. • Confidence in MTD is usually poor. • Treat 3 patients at dose K • If 0 patients experience dose-limiting toxicity (DLT), escalate to dose K+1 • If 2 or more patients experience DLT, de-escalate to level K-1 • If 1 patient experiences DLT, treat 3 more patients at dose level K • If 1 of 6 experiences DLT, escalate to dose level K+1 • If 2 or more of 6 experiences DLT, de-escalate to level K-1

33. Continual Reassessment Method • Allows statistical modeling of optimal dose: dose-response relationship is assumed to behave in a certain way • Can be based on “safety” or “efficacy” outcome (or both). • Design aims to determine an optimal dose, given a desired toxicity or efficacy level, and does so in an efficient way. • This design REALLY requires a statistician throughout the trial. • Example: Phase I/II trial of Samarium 153 in High Risk Osteogenic Sarcoma (Schwartz)

34. CRM history in brief • Originally devised by O’Quigley, Pepe and Fisher (1990) where dose for next patient was determined based on responses of patients previously treated in the trial • Due to safety concerns, several authors developed variants • Modified CRM (Goodman et al. 1995) • Extended CRM [2 stage] (Moller, 1995) • Restricted CRM (Moller, 1995) • and others ….

35. Basic Idea of CRM

36. Modified CRM (Goodman, Zahurak, and Piantadosi, Statistics in Medicine, 1995) • Carry-overs from standard CRM • Mathematical dose-toxicity model must be assumed • To do this, we need to think about the dose-response curve and create a preliminary model. • We CHOOSE the level of toxicity that we desire for the MTD (p = 0.30) • At end of trial, we can estimate a dose response curve. • “prior distribution”(mathematical subtlety)

37. Modified CRM by Goodman, Zahurak, and Piantadosi(Statistics in Medicine, 1995) • Modifications by Goodman et al. • Use ‘standard’ dose escalation model until first toxicity is observed: • Choose cohort sizes of 1, 2, or 3 • Use standard ‘3+3’ design (or, in this case, ‘2+2’) • Upon first toxicity, fit the dose-response model using observed data • Estimate  • Find dose that is closest to toxicity of 0.3. • Does not allow escalation to increase by more than one dose level. • De-escalation can occur by more than one dose level. • Dose levels are discrete: must be rounded off to closest level

38. ExampleSamarium study with cohorts of size 2: 2 patients treated at dose 1 with 0 toxicities 2 patient treated at dose 2 with 1 toxicity  Fit CRM using equation below • Estimated  = 0.77 • Estimated dose for • next patient is 2.0 • Use dose level 2 • for next cohort.

39. Example Samarium study with cohorts of size 2: 2 patients treated at dose 1 with no toxicities 4 patients treated at dose 2 with 1 toxicity  Fit CRM using equation on earlier slide • Estimated  = 0.88 • Estimated dose for next • patient is 2.54 • Round up to dose • level 3 for next cohort.

40. Example Samarium study with cohorts of size 2: 2 patients treated at dose 1 with no toxicities 4 patients treated at dose 2 with 1 toxicity 2 patients treated at dose 3 with 1 toxicity  Fit CRM using equation on earlier slide • Estimated  = 0.85 • Estimated dose for next • patient is 2.47 • Use dose level 2 • for next cohort.

41. Example Samarium study with cohorts of size 2: 2 patients treated at dose 1 with no toxicities 6 patient treated at dose 2 with 1 toxicity 2 patients treated at dose 3 with 1 toxicity  Fit CRM using equation on earlier slide • Estimated  = 0.91 • Estimated dose for next • patient is 2.8 • Use dose level 3 • for next cohort. • Etc.

42. Longitudinal Studies • Multiple observations per individual over time • Sample size calculations are HARD • But, analysis is also complex • Standard assumption of “basic” statistical methods and models is that observations are independent • With longitudinal data, we have “correlated” measures within individuals

43. Study of Autism in Young Children (Landa) • Autism is usually diagnosed at age 3 • But, there is evidence that there are earlier symptoms that are indicative of autism • Children at high risk of autism (kids with older autistic siblings) and “controls” were observed at 6 months, 14 months, and 24 months for symptoms (Mullen) • Prospective study • Children were diagnosed at 36 months into three groups. • ASD (autism-spectrum disorder) • LD (learning disabled) • Unaffected • Earlier symptoms were compared to see if certain symptoms could predict diagnosis.

44. P-values were included in original table!

45. Statistical modeling can help! • Previous table was hard to draw conclusions from • Each time point was analyzed separately, and within time points, groups were compared. • Use some reasonable assumptions to help interpretation • Children have “growth trajectories” that are continuous and smooth • Observations within the same child are correlated.

47. Conclusions are much easier • The models used to make the graphs are somewhat complicated • But, they are “behind the scenes” • The important information is presented clearly and concisely • ANOVA approach does not “summarize” data

48. Concluding Remarks • Involve your statistician as soon as you begin to plan your study • Things statisticians do not like: • Being contacted a few days before grant/protocol/proposal is due • Rewriting inappropriate statistical sections • Analyzing data from a poorly designed trial • Statisticians have a lot to add • A “fresh” perspective on your study • A more efficient study!