Presentation is loading. Please wait.

Presentation is loading. Please wait.

Issues in Analysis of Randomized Clinical Trials

Similar presentations

Presentation on theme: "Issues in Analysis of Randomized Clinical Trials"— Presentation transcript:

1 Statistics 542 Introduction to Clinical Trials Issues in Analysis of Randomized Clinical Trials

2 Issues in Analysis of Randomized Clinical Trials
Reference: May, DeMets et al (1981) Circulation 64: Peto et al (1976) British Journal of Cancer

3 Methods to Minimize Bias
Sources of Bias 1. Patient selection 2. Treatment assignment 3. Patient Evaluation 4. Data Analysis Methods to Minimize Bias 1. Randomized Controls 2. Double blind (masked) 3. Analyze what is randomized

4 What Data Should Be Analyzed?
Basic Intention-to-Treat Principle Analyze what is randomized! All subjects randomized, all events during follow-up Randomized control trial is the “gold” standard” Definitions Exclusions Screened but not randomized Affects generalizability but validity OK Withdrawals from Analysis Randomized, but not included in data analysis Possible to introduce bias!

5 Patient Closeout ICH E9 Glossary
“Intention-to-treat principle - …It has the consequence that subjects allocated to a treatment group should be followed up, assessed, and analyzed as members of that group irrespective of their compliance with the planned course of treatment.”

6 Intention To Treat (ITT) Principle
Analyze all subjects randomized & all events Beware of “look alikes” Modified ITT: Analyze subjects who get some intervention Per Protocol: Analyze subjects who comply according to the protocol

7 Patient Withdrawn in Analysis (1)
Common Practice s Over 3 years, 37/109 trials in New England Journal of Medicine published papers with some patient data not included Typical Reasons Given a. Patient ineligible (in retrospect) b. Noncompliance c. Competing events d. Missing data

8 Patient Withdrawn in Analysis (2)
A. Patient INELIGIBLE After randomization, discover some patients did not in fact meet entry criteria Concern ineligible patients may dilute treatment effect Temptation to withdraw ineligibles Withdrawl of ineligible patients, post hoc, may introduce bias

9 Betablocker Heart Attack Trial (JAMA, 1982)
3837 post MI patients randomized 341 patients found by Central Review to be ineligible Results % Mortality Propranolol Placebo Eligible Ineligible Best Total  In the ineligible patients, treatment works best

10 Anturane Reinfarction Trial (1980) NEJM
Randomized, double blind, placebo controlled Anturane Placebo Total Randomized Ineligible Reasons for ineligible 1/3 - time since MI: < 25 days or > 35 days 1/3 - enzymes not elevated 1/3 - other: age, enlarged heart, prolonged hospitalization, .… Number ineligible about the same in each treatment group BUT

11 Anturane Reinfarction Trial (1980)
1629 patients randomized 1631 entered, but two patients randomized twice Need to delete 03013, 17008 Use first randomization! Declared post hoc 71 “ineligible” patients

12 Anturane Reinfarction Trial (1980)
Placebo Anturane Total All Ineligible Eligible < 7 day rule Analyzable subjects (Table 3) Analyzable Deaths - Within 7 days of being off drug

13 1980 Anturane Mortality Results
Anturane Placebo P-Value Randomized 74/813 (9.1%) 89/816 (10.9%) 0.20 “Eligible” 64/775 (8.3%) 85/783 (10.9%) 0.07 “Ineligible” 10/38 (26.3%) 4/33 (12.1%) 0.12 P-Values for eligible vs ineligible Reference: Temple & Pledger (1980) NEJM, p. 1488

14 1980 Anturane Mortality Results
Anturane Placebo Withdrawn “Early” discontinuation 4 3 “Late” discontinuation 6 1

15 Total Mortality Anturane Reinfarction Trial (1980)
I All Pts All Deaths Random Deaths * NEJM accounts for only Anturane Placebo Total * P = (Table 3+6) II Subjects - Exclude 71 Non-eligibles All Deaths Random Deaths “71" Anturane (10) Placebo (4) Total P = 0.07

16 Total Mortality Anturane Reinfarction Trial (1980)
III Subjects - Exclude 71 Non-eligibles + 30<7 days All Deaths Random Deaths Anturane Placebo Total IV Subjects Analyzable Deaths Random Deaths Anturane Placebo Total P = 0.076

17 Total Mortality Anturane Reinfarction Trial (1980)
Consider Patients Excluded I. < 7 day rule - 30 pts Alive Dead Total Placebo Anturane Total

18 Total Mortality Anturane Reinfarction Trial (1980)
II "ineligibles" Alive Dead Total Placebo Anturane Total

19 Anturane Sudden Death (SD)
I. All Patients (N = 1629) Randomized NDA-SDs NEJM-SDs Placebo Anturane Total P-value 11 additional SD's were defined from submission of NDs to publications II Exclude 71 Protocol Violators (N = 1558) Placebo Anturane Total P-value Difference of 8 SD's

20 Anturane Sudden Death (SD) for Total Follow-up
III. Exclude 71 Protocol Violators & 30 7 Day Rule Violators (N = 1528) Randomized NDA-SDs NEJM-SDs Placebo Anturane Total P-value * Information not necessarily given in NEJM articlebut used to prepare tables presented

21 Comparison of the Mortality Experience for
Anturane Analysis Table D Article Comparison of the Mortality Experience for the 4 Patient Groups Percent Mortality Patient Group Anturane Placebo P-value (45/806) (61/814) 0.10 (41/781) 7.4 (58/786) 0.07 (35/768) 7.4 (58/779) 0.01 (32/733) 7.1 (53/742) 0.02 Article ' (25/733) 5.9 (44/742) + Number of deaths/number at risk

22 ART (NEJM, 1978) Comparisons of the Mortality Experience for the 73 Patients with "Objective" and "Subjective" Baseline Exclusions Groups Compared % Mortality Placebo vs. Anturane in the 73** 8.6 (3/35)* 26.3 (10/38) 73 vs. 1547*** (13/73) 6.0 (93/1547) (Both Treatment Groups) 73 vs (Anturane Group) 26.3 (10/38) 4.6 (35/768) 73 vs (Placebo Group) 8.6 (3/35) 7.5 (58/779) * Number of deaths/number at risk ** 73 refers to the group of 73 patients with "objective" or "subjective" reasons at baseline for exclusion *** 1547 refers to the total group of randomized patients with the 73 patients with objective and subjective baseline exclusions removed

23 ART (NEJM, 1978) P-Values Using Two Techniques for Survival Curve Comparisons of the Groups
Groups Compared Mantel-Haenszel Gehan Method Method Placebo vs. Anturane in the 73 vs. 1547 (Both Treatment Groups) 73 vs (Anturane Only) < < 73 vs (Placebo Only)

24 Acceptable Policies For Ineligible Subjects
1. Delay randomization, confirm eligibility and allow no withdrawals (e.g. AMIS) (Chronic Studies) 2. Accept ineligibles, allow no withdrawals (e.g. BHAT, MILIS) (Acute Studies) 3. Allow withdrawals if: a. Procedures defined in advance b. Decision made early (before event) c. Decision independent and blinded d. Use baseline covariates only (two subgroups) e. Analysis done with and without

B. WITHDRAWL FOR NON-COMPLIANCE References: Sackett & Gent (1979) NEJM, p. 1410 Coronary Drug Project (1980) NEJM, p. 1038 Two Types of Trials 1. Management - "Intent to Treat" Principle - Compare all subjects, regardless of compliance 2. Explanatory - Estimate optimum effect, understand mechanism - Analyze subjects who fully comply WITHDRAWALS FOR NON-COMPLIANCE MAY LEAD TO BIAS!

26 Breast Cancer Adjuvant Therapy Probability of Disease Free Survival for Years Post Mastectomy (Method I) Redmond et al (1983) Cancer Treatment Report

27 Breast Cancer Adjuvant Therapy Probability of Disease Free Survival for Years Post Mastectomy (Method II) Redmond et al (1983) Cancer Treatment Report

28 Breast Cancer Adjuvant Trial
Results using stratification by compliance analysis can be re-ordered according to definition Both previous graphs are for the placebo arm Lesson: Compliance is an outcome & analysis of one outcome, stratified by another, is highly vulnerable to bias

29 Cancer Trial (5-FU & Radiation) Gastric Carcinoma
Reference: Moertel et al. (Journal of Clinical Oncology, 1984) 62 patients randomized No surgical adjuvant therapy vs. 5-FU and radiation 5 year survival results Randomized Percent (%) Treatment 23% P < 0.05 No Treatment 4%

30 Cancer Trial (5-FU & Radiation) Gastric Carcinoma
According to treatment received 5 year survival Received % Survival Treatment 20% Refused Treatment 30% NS Control 4%

31 Example: Coronary Drug Project 5-Year Mortality
Clofibrate Placebo N % Deaths N % Deaths Total (as reported) By Compliance < 80% > 80% Adjusting for 40 covariates had little impact Compliance is an outcome Compliers do better, regardless of treatment

32 Example: Coronary Drug Project 2-Year Mortality
Compliance Assessed Estrogen Placebo N % Deaths N % Deaths Total < 80% > 80% Comments Higher % of estrogens patients did not comply Beneficial to be randomized to estrogen & not take it (6.1% vs. 9.9%) Best to be randomized to placebo & comply (4.8%)

33 Example: Wilcox et al (1980) Trial, BMJ 6-Week Mortality
Propranolol Atenolol Placebo N % Deaths N % Deaths N % Deaths Total Compliers Non-compliers Comments Compliers did better than placebo Treatment non-compliers did worse than placebo Placebo non-compliers only slightly worse than compliers Analysis by compliers overestimates benefit

34 Aspirin Myocardial Infarction Study (AMIS)
% Mortality Compliance Aspirin Placebo Good Poor Total

35 Summary of Compliance No consistent pattern
Example Non-compliance Did Worse CDP Clofibrate, AMIS Both Treatment & Control CDP Estrogen Control Only Beta-blocker, Wilcox Two Treatments, Not Control Compliance an outcome, not always independent of treatment Withdrawal of non-compliers can lead to bias Non-compliers dilute treatment Try hard not to randomize non-compliers

36 II. Competing Events Subject may be censored from primary event by some other event (e.g. cancer vs. heart disease) Must assume independence If cause specific mortality used, should also look at total death If non-fatal event is primary, should also look at total death and non-fatal event Problem for some response measures

37 III. Problem of Definitions
Cause specific definitions hard to apply Example: Anturane Reinfarction Trail (ART) (NEJM, 1980) Sudden Death Classification Anturane Placebo P-value ART 30/ / Another Committee 28/812 39/

38 Anturane Reinfarction Trial Sudden Death
Category Source Placebo Anturane P-value All patients & all NEJM 48/ / sudden deaths AC 39/ / "Eligible" patients & NEJM 46/ / all sudden deaths AC 37/ / Problem of cause specific definitions AC = Another review committee

39 IV. "Wrong", Inconsistent, Outlying Data
"Wrong" or "outlying" data may in fact be real Decisions must be made blind of group assignment All modifications or withdrawals must be documented

40 V. Missing Outcome Data Design with zero
missingness may be associated with treatment for analysis, data are not missing at random even if same number missing, missing may be for different reason in each treatment group Implement with minimum possible Analyze exploring different approaches if all, or most, agree, then more persuasive

41 “Best” and “Worst” Case Analyses
Treatment Control Total Events Lost to Follow-up "Best" Case "Worst" Case

42 VI. Poor Quality Data

43 Poor Quality Data (1) Lost to Follow-up
(enforced withdrawals)  NO DATA: PROBLEMS: Not necessarily independent of treatment Raises questions about study conduct

44 Poor Quality Data (2) SOLUTIONS: Keep to a minimum
Easiest if vital status is the outcome Hardest if the response variables are time-related measures requiring a hospital or clinic visit Censor at the time lost Can be done in survival analysis Assumes independence of treatment

45 Poor Quality Data (3) SOLUTIONS:
3. Estimate missing data using previous data or averages 4. “Best” case and “worst” case analyses

46 VII. Poor Clinic Performance in a Multicenter Study
If randomization was stratified by clinic, then withdrawal of a clinic is theoretically valid Withdrawal must be done independent of the outcome at that clinic

47 Mortality in Aspirin Myocardial Infarction Study (AMIS)
Aspirin Placebo P-value All 30 Centers 246/ / 7 “Selected” Centers < 0.01 In “selected” centers, aspirin showed superiority

48 Mortality in Beta-Blocker Heart Attack Trial (BHAT)
Propranolol Placebo P-value All 32 Centers / /1921 < 0.01 Cox adjusted Z = 3.05 6 “Selected” Centers < 0.05 In “selected” centers, propranolol worse

49 VIII. Special Counting Rules
Events beyond a specified number of days after treatment stopped not counted "non-analyzable" Examples 1. "7 Day Rule" Anturane (1978) NEJM 2. "28 Day Rule" Timolol (1981) NEJM If used, must Specify in advance Be a long period to insure termination not related to outcome Analyze results both ways

50 IX. Fishing or Dichotomizing Outcomes
Common practice to define a response (S,F) from a non-dichotomous variable By changing our definition, we can alter results Thus, definitions stated in advance Definitions should be based on external data

51 Dichotomizing Outcomes
Example Heart Rate Trt A Trt B Subject Pre Post  Pre Post  ... Mean

52 Three Possible Analyses (1)
Change  Treatment A Treatment B P-Value 1. F = < S = >

53 Three Possible Analyses (2)
Change  Treatment A Treatment B P-Value 1. F = < S = > 2. F = < S = >

54 Three Possible Analyses (3)
Change  Treatment A Treatment B P-Value 1. F = < S = > 2. F = < S = > 3. F = < S = >

55 X. Time Dependent Covariate Adjustment
Classic covariate adjustment uses baseline prognostic factors only Adjust for Imbalance Gain Efficiency Adjustment by time dependent variates not recommended in clinical trials (despite Cox time dependent regression model) Habit from epidemiology studies

56 Coronary Drug Project 5-Year Mortality
Example Baseline Cholesterol % Deaths Cholesterol Change Clofibrate Placebo < 250mg%* Fall < 250 Rise > 250 mg% Fall > 250 ** Rise Little change in placebo group Best to have a. Low cholesterol getting lower * b. High cholesterol getting higher **

57 Example: Cancer Trials
A common practice to compare survival on patients with a tumor response Problem is that patient must first survive to be a responder length - bias sampling

58 Cancer Trials (1) Advanced Breast Cancer: Surgery vs. Medicine
Santen et al. (1981) NEJM (Letter to editor, Paul Meier, U of Chicago) A randomized clinical trial comparing surgical adrenalectomy vs. drug therapy in women with advanced breast cancer 17 pts withdrawn from surgery group 10 pts withdrawn from medical group

59 Cancer Trials (2) Reasons Medical group (10 pts)
2 stopped taking their drugs 5 drug toxicity Surgical group (17 pts) 7 later refused surgery 8 rapid progression precluding surgery No follow-up data on these 27 pts presented

60 XI. Subgroup Analyses

61 False Positive Rates The greater the number of subgroups analyzed separately, the larger the probability of making false positive conclusions. No. of Subgroups False Positive Rate

62 Subgroup Analyses Focusing on a particular “significant” subgroup can be risky Due to chance Results not consistent Estimates not precise due to small sample size

63 MERIT Total Mortality


65 MERIT (AHJ, 2001)

66 Praise I Ref: NEJM, 1996 Amlodipine vs. placebo NYHA class II-III
Randomized double-blind Mortality/hospitalization outcomes Stratified by etiology (ischemic/non-ischemic) 1153 patients


68 PRAISE I - Interaction Overall P = 0.07 Etiology by Trt Interaction
Ischemic P = NS Non-Ischemic P < 0.001

69 PRAISE I - Ischemic

70 PRAISE I – Non- Ischemic

71 PRAISE II Repeated non-ischemic strata Amlodipine vs. placebo
Randomized double-blind 1653 patients Mortality outcome RR  1.0

72 Three Views Ignore subgroups and analyze only by treatment groups.
Plan for subgroup analyses in advance. Do not “mine” data. Do subgroup analyses However view all results with caution.

73 Analysis Issues Summary
Important not to introduce bias into the analysis ITT principle is critical Important to have “complete” follow-up Off treatment is not off study

Download ppt "Issues in Analysis of Randomized Clinical Trials"

Similar presentations

Ads by Google