How to design and interpret controlled clinical trials “the dark side of the moon” “How to session” ESH June 2005 Andreas Pittaras MD.

How to design and interpret controlled clinical trials “the dark side of the moon” “How to session” ESH June 2005 Andreas Pittaras MD

E. FREIS 1912-2005 The father of the first multicenter, double- blinded, random trial of cardiovascular drugs, VA Cooperative Study on Antihypertensive Agents

10.00 new randomized trials every year >350.000 trials General internists would need to read 20 articles a day all year round to maintain present knowledge Systematic reviews and guidelines reduces this problem

“the aim of science (…clinical trial) is not to open a door to endless wisdom, but to put a limit to endless error” -Bertolt Brecht

Do we wear the same eyeglasses ? Clinical Trials

Clinical Studies: Essential Questions Was the study original? Whom is the study about? Was the design of the study sensible? Was systematic bias avoided or minimized? Was the study large enough, and continued for long enough, to make the results credible?

Clinical Studies: Essential Questions Was the study original?

Is there any similar study? Is this study bigger, continued for longer, or otherwise more substantial than previous one(s)? Is the methodology of this study any more rigorous (in particular, does it address any specific methodological criticisms of previous studies)?

Will the numerical results of this study add significantly to a meta-analysis of previous studies? Is the population that was studied different in any way (has the study looked at different ages, sex, or ethnic groups than previous studies)? Is the clinical issue addressed of sufficient importance, and is there sufficient doubt in the minds of the public or key decision makers, to make new evidence “politically” desirable even when it is not strictly scientifically necessary?

Clinical Studies: Essential Questions Whom is the study about?

How were the subjects recruited ? advertisement local newspaper, primary care, veterans, homeless people etc Who was included in the study? coexisting illness, local language, other medication, illiterate people etc (the results of studies of new drugs in 23 yo healthy male volunteers will not be applicable to the average elderly women) Who was excluded from the study? A study may be restricted to pts with moderate or severe CHF, which could lead to false conclusions about mild CHF. Hospital outpatients studies have different disease spectrum from the primary care Were the subjects studied in real life circumstances? doubt on the applicability of findings to your own practice

Clinical Studies: Essential Questions was the design of the study sensible?

What specific intervention or other maneuver was being considered, and what was it being compared with ? It is tempting to take published statements at face value, but authors frequently misrepresent (usually subconsciously rather than deliberately) what they actually did, and they overestimate its originality and potential importance. …… examples of problematic descriptions in the method section of a clinical trial……

What the authors said What they should have said (or should have done)An example of: "We measured how often GPs ask patients whether they smoke.""We looked in patients' medical records and counted how many had had their smoking status recorded." Assumption that medical records are 100% accurate. "We measured how doctors treat low back pain.""We measured what doctors say they do when faced with a patient with low back pain." Assumption that what doctors say they do reflects what they actually do. "We compared a nicotine-replacement patch with placebo.""Subjects in the intervention group were asked to apply a patch containing 15 mg nicotine twice daily; those in the control group received identical-looking patches." Failure to state dose of drug or nature of placebo. "We asked 100 teenagers to participate in our survey of sexual attitudes.""We approached 147 white American teenagers aged 12-18 (85 males) at a summer camp; 100 of them (31 males) agreed to participate." Failure to give sufficient information about subjects. (Note in this example the figures indicate a recruitment bias towards females.) "We randomized patients to either 'individual care plan' or 'usual care'.""The intervention group were offered an individual care plan consisting of...; control patients were offered...." Failure to give sufficient information about intervention. (Enough information should be given to allow the study to be repeated by other workers.) "To assess the value of an educational leaflet, we gave the intervention group a leaflet and a telephone helpline number. Controls received neither." If the study is purely to assess the value of the leaflet, both groups should have been given the helpline number. Failure to treat groups equally apart form the specific intervention. "We measured the use of vitamin C in the prevention of the common cold."A systematic literature search would have found numerous previous studies on this subject 14 Unoriginal study.

What the authors said What they should have said (or should have done) An example of: "We measured how often GPs ask patients whether they smoke.""We looked in patients' medical records and counted how many had had their smoking status recorded." Assumption that medical records are 100% accurate. "We measured how doctors treat low back pain.""We measured what doctors say they do when faced with a patient with low back pain." Assumption that what doctors say they do reflects what they actually do. "We compared a nicotine-replacement patch with placebo.""Subjects in the intervention group were asked to apply a patch containing 15 mg nicotine twice daily; those in the control group received identical-looking patches." Failure to state dose of drug or nature of placebo. "We asked 100 teenagers to participate in our survey of sexual attitudes.""We approached 147 white American teenagers aged 12-18 (85 males) at a summer camp; 100 of them (31 males) agreed to participate." Failure to give sufficient information about subjects. (Note in this example the figures indicate a recruitment bias towards females.) "We randomized patients to either 'individual care plan' or 'usual care'.""The intervention group were offered an individual care plan consisting of...; control patients were offered...." Failure to give sufficient information about intervention. (Enough information should be given to allow the study to be repeated by other workers.) "To assess the value of an educational leaflet, we gave the intervention group a leaflet and a telephone helpline number. Controls received neither." If the study is purely to assess the value of the leaflet, both groups should have been given the helpline number. Failure to treat groups equally apart form the specific intervention. "We measured the use of vitamin C in the prevention of the common cold."A systematic literature search would have found numerous previous studies on this subject 14 Unoriginal study.

What the authors saidWhat they should have said (or should have done) An example of: "We measured how often GPs ask patients whether they smoke.""We looked in patients' medical records and counted how many had had their smoking status recorded." Assumption that medical records are 100% accurate. "We measured how doctors treat low back pain.""We measured what doctors say they do when faced with a patient with low back pain." Assumption that what doctors say they do reflects what they actually do. "We compared a nicotine-replacement patch with placebo.""Subjects in the intervention group were asked to apply a patch containing 15 mg nicotine twice daily; those in the control group received identical-looking patches." Failure to state dose of drug or nature of placebo. "We asked 100 teenagers to participate in our survey of sexual attitudes.""We approached 147 white American teenagers aged 12-18 (85 males) at a summer camp; 100 of them (31 males) agreed to participate." Failure to give sufficient information about subjects. (Note in this example the figures indicate a recruitment bias towards females.) "We randomized patients to either 'individual care plan' or 'usual care'.""The intervention group were offered an individual care plan consisting of...; control patients were offered...." Failure to give sufficient information about intervention. (Enough information should be given to allow the study to be repeated by other workers.) "To assess the value of an educational leaflet, we gave the intervention group a leaflet and a telephone helpline number. Controls received neither." If the study is purely to assess the value of the leaflet, both groups should have been given the helpline number. Failure to treat groups equally apart form the specific intervention. "We measured the use of vitamin C in the prevention of the common cold."A systematic literature search would have found numerous previous studies on this subject 14 Unoriginal study.

What the authors said What they should have said (or should have done)An example of: "We measured how often GPs ask patients whether they smoke." "We looked in patients' medical records and counted how many had had their smoking status recorded." Assumption that medical records are 100% accurate. "We measured how doctors treat low back pain.""We measured what doctors say they do when faced with a patient with low back pain." Assumption that what doctors say they do reflects what they actually do. "We compared a nicotine-replacement patch with placebo.""Subjects in the intervention group were asked to apply a patch containing 15 mg nicotine twice daily; those in the control group received identical-looking patches." Failure to state dose of drug or nature of placebo. "We asked 100 teenagers to participate in our survey of sexual attitudes.""We approached 147 white American teenagers aged 12-18 (85 males) at a summer camp; 100 of them (31 males) agreed to participate." Failure to give sufficient information about subjects. (Note in this example the figures indicate a recruitment bias towards females.) "We randomized patients to either 'individual care plan' or 'usual care'.""The intervention group were offered an individual care plan consisting of...; control patients were offered...." Failure to give sufficient information about intervention. (Enough information should be given to allow the study to be repeated by other workers.) "To assess the value of an educational leaflet, we gave the intervention group a leaflet and a telephone helpline number. Controls received neither." If the study is purely to assess the value of the leaflet, both groups should have been given the helpline number. Failure to treat groups equally apart form the specific intervention. "We measured the use of vitamin C in the prevention of the common cold."A systematic literature search would have found numerous previous studies on this subject 14 Unoriginal study.

What the authors said What they should have said (or should have done) An example of: "We measured how often GPs ask patients whether they smoke." "We looked in patients' medical records and counted how many had had their smoking status recorded." Assumption that medical records are 100% accurate. "We measured how doctors treat low back pain.""We measured what doctors say they do when faced with a patient with low back pain." Assumption that what doctors say they do reflects what they actually do. "We compared a nicotine-replacement patch with placebo.""Subjects in the intervention group were asked to apply a patch containing 15 mg nicotine twice daily; those in the control group received identical-looking patches." Failure to state dose of drug or nature of placebo. "We asked 100 teenagers to participate in our survey of sexual attitudes.""We approached 147 white American teenagers aged 12-18 (85 males) at a summer camp; 100 of them (31 males) agreed to participate." Failure to give sufficient information about subjects. (Note in this example the figures indicate a recruitment bias towards females.) "We randomized patients to either 'individual care plan' or 'usual care'.""The intervention group were offered an individual care plan consisting of...; control patients were offered...." Failure to give sufficient information about intervention. (Enough information should be given to allow the study to be repeated by other workers.) "To assess the value of an educational leaflet, we gave the intervention group a leaflet and a telephone helpline number. Controls received neither." If the study is purely to assess the value of the leaflet, both groups should have been given the helpline number. Failure to treat groups equally apart form the specific intervention. "We measured the use of vitamin C in the prevention of the common cold."A systematic literature search would have found numerous previous studies on this subject 14 Unoriginal study.

What the authors said What they should have said (or should have done)An example of: "We measured how often GPs ask patients whether they smoke.""We looked in patients' medical records and counted how many had had their smoking status recorded." Assumption that medical records are 100% accurate. "We measured how doctors treat low back pain.""We measured what doctors say they do when faced with a patient with low back pain." Assumption that what doctors say they do reflects what they actually do. "We compared a nicotine-replacement patch with placebo.""Subjects in the intervention group were asked to apply a patch containing 15 mg nicotine twice daily; those in the control group received identical-looking patches." Failure to state dose of drug or nature of placebo. "We asked 100 teenagers to participate in our survey of sexual attitudes." "We approached 147 white American teenagers aged 12-18 (85 males) at a summer camp; 100 of them (31 males) agreed to participate." Failure to give sufficient information about subjects. (Note in this example the figures indicate a recruitment bias towards females.) "We randomized patients to either 'individual care plan' or 'usual care'.""The intervention group were offered an individual care plan consisting of...; control patients were offered...." Failure to give sufficient information about intervention. (Enough information should be given to allow the study to be repeated by other workers.) "To assess the value of an educational leaflet, we gave the intervention group a leaflet and a telephone helpline number. Controls received neither." If the study is purely to assess the value of the leaflet, both groups should have been given the helpline number. Failure to treat groups equally apart form the specific intervention. "We measured the use of vitamin C in the prevention of the common cold."A systematic literature search would have found numerous previous studies on this subject 14 Unoriginal study.

What the authors said What they should have said (or should have done) An example of: "We measured how often GPs ask patients whether they smoke.""We looked in patients' medical records and counted how many had had their smoking status recorded." Assumption that medical records are 100% accurate. "We measured how doctors treat low back pain.""We measured what doctors say they do when faced with a patient with low back pain." Assumption that what doctors say they do reflects what they actually do. "We compared a nicotine-replacement patch with placebo.""Subjects in the intervention group were asked to apply a patch containing 15 mg nicotine twice daily; those in the control group received identical-looking patches." Failure to state dose of drug or nature of placebo. "We asked 100 teenagers to participate in our survey of sexual attitudes." "We approached 147 white American teenagers aged 12-18 (85 males) at a summer camp; 100 of them (31 males) agreed to participate." Failure to give sufficient information about subjects. (Note in this example the figures indicate a recruitment bias towards females.) "We randomized patients to either 'individual care plan' or 'usual care'.""The intervention group were offered an individual care plan consisting of...; control patients were offered...." Failure to give sufficient information about intervention. (Enough information should be given to allow the study to be repeated by other workers.) "To assess the value of an educational leaflet, we gave the intervention group a leaflet and a telephone helpline number. Controls received neither." If the study is purely to assess the value of the leaflet, both groups should have been given the helpline number. Failure to treat groups equally apart form the specific intervention. "We measured the use of vitamin C in the prevention of the common cold."A systematic literature search would have found numerous previous studies on this subject 14 Unoriginal study.

What outcome was measured, and how? If you had an incurable disease, testing a new drug, you would measure the efficacy of the drug in terms of whether it made you live longer (and perhaps, whether life was worth living given your condition and any side effects of the medication) The measurement of symptomatic effects (pain), functional effects (mobility), psychological effects (anxiety), or social effects (inconvenience) of an intervention has even more problems. What is important in the eyes of the doctor may not be valued so highly by the patient, and vice versa.

Clinical Studies: Essential Questions Was systematic bias avoided or minimized?

The aim : groups as similar as possible except for the particular difference being examined Receive same explanations Have same contacts with health professionals Be assessed the same number of times Using the same outcome measures

Different study designs to reduce systematic bias Randomized controlled trials Non-randomized controlled clinical trials Cohort studies Case-control studies

Randomized double-blind controlled trials “Gold standard” The two treatments are investigated concurrently Allocation of treatments to patients is by a random process Neither the patient nor the clinician knows which treatment was received “Single blind”: only the patient is unaware

Random allocation : same chance of receiving either treatment, and is thus unbiased by definition Minimization (each pt takes automatically the treatment which leads to less imbalance; alternative in small trials,) Systematic allocation (pseudo-random; even vs odd days groups; open to abuse) Non-random concurrent controls ( active vs control of ineligible + refusers; volunteer bias) Historical controls ( a single group of new treatment vs a group previously treated with other alternative treatment)

Alternative designs Parallel group design (two different groups are studied concurrently) Crossover design Within group (paired) comparisons Sequential designs Factorial designs Adaptive designs Zelen’s design

Sequential design Parallel groups are studied, but the trial continues until the clear benefit of one treatment, or it is unlikely that any difference will emerge. Will be shorter than fixed length trials The data are analyzed after each pt’s results become available Blinding problems; ethical difficulties Group sequential trial : a useful variation; data analysis after each block of patients are available (early termination)

Factorial designs Two treatments, A & B, are simultaneously compared with each other and with a control. Pts are divided into four groups, who receive the control treatment, A only, B only, and both A&B. Allows the investigation of the “synergy” between A & B

Clinical Studies: Essential Questions Was assessment “blind”?

“Blind” assessment? People who assess outcome know the patient’s group -Judge whether someone is still clinically in heart failure -Say whether an x ray is “improved” from last time -recheck a high BP measurement in active group -BB vs ACEi or ARBs or Diuretics(<HR, <K+) -CCB vs others (pedal edema)

Clinical Studies: Essential Questions Was the study large enough, and continued for long enough, to make the results credible?

Sample Size Big enough to have a high chance of detecting a worthwhile effect if it exists Be reasonably sure that no benefit exists if its not found in the trial

Errors defined Type I error (α) : The probability of detecting a statistically significant difference when the treatments are in reality equally effective (the chance of false-positive result) Type II error (β): :The probability of not detecting a statistically significant difference when a difference of a given magnitude in reality exists (the chance of a false-negative result) Power (1-β): The probability of detecting a statistically significant difference when a difference of a given magnitude really exists

The simplest approximate sample size formula for binary outcomes, assuming α=0.05, power=0.90, and equal sample sizes in the two groups n=n= 10.51 [(R+1)- p ₂ (R²+1)] p ₂ (1-R)² n : the sample size in each of the groups p ₁ : event rate in the treatment group p ₂ : event rate in the control group R : risk ratio (p ₁ /p ₂ )

Power (1-β) α (type I error)0.800.900.95 0.05 7.8510.5113.00 0.01 11.6814.8817.82

The simplest approximate sample size formula for binary outcomes, assuming α=0.05, power=0.90, and equal sample sizes in the two groups N=962 = 10.51 [(0.60+1)-0.10(0.60²+1)] 0.10(1-0.60)² n : the sample size in each of the groups p ₁ : 0.06 ( 6% event rate in the treatment group) p ₂ :0.10 (estimate 10% event rate in the control group) R :0.60=6%/10% (to detect 40% reduction (p ₁ /p ₂ )

Approximate relative trial sizes for different levels of “ α” and “ power” Power (1-β) α (type I error) 0.500.800.900.99 0.05 100200270480 0.01 170300390630 0.001 280440540820

Duration of follow up The study must continue long enough for the effect of intervention to be reflected in the outcomes. A study of a new painkiller on the postoperative pain may only need a follow up period of 48h. The effect of nutritional supplements in the preschool years on the final height needs decades. Events in newly diagnosed DM need >10 years

Completeness of follow up (“drop out of”) Not receiving the tablets Missing their interim checkups Loss of patient motivation Side effects Clinical reasons ( concurrent illness, pregnancy) Incorrect entry Death.

Different results in trials High-dose oxygen therapy in neonates Antiarrhythmic drugs after MI Fluoride treatment for osteoporosis Bed rest in twin pregnancy HRT in vascular prevention High-dose aspirin for carotid endarterectomy b-blockers in heart failure Digoxin after MI

Interpretation “Tips” of results p <0.05 means by chance <1:20 “significant” p<0.01 by chance <1:100 “highly significant” CI “confidence interval” around a result: indicates the limits within which the “real” difference is likely to lie Every r value should be accompanied by a p value or a CI

Interpretation “Tips” of results Relative Risk of death Relative Risk Reduction Absolute Risk Reduction Number needed to treat Odds Ratio

10.00 new randomized trials every year >350.000 trials General internists would need to read 20 articles a day all year round to maintain present knowledge Systematic reviews and guidelines reduces this problem 30-40% of patients do not receive care according to present scientific evidence 20-25% of care provided, is not needed or is potentially harmful

Common clinician concerns about trials, subgroups, meta-analyses, and risk “Could my patient have been randomized in this trial? If so the results are applicable; if not, they may not be” “Is my patient so different from those in the trial that its results cannot help me make my treatment decision?”

Source Population Eligible Population Participants Exposure or Intervention Comparison or Control Outcomes +_+_ +_+_ Nested triangles : Different Population with a Common condition

How to design and interpret controlled clinical trials “the dark side of the moon” “How to session” ESH June 2005 Andreas Pittaras MD.

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How to design and interpret controlled clinical trials “the dark side of the moon” “How to session” ESH June 2005 Andreas Pittaras MD.

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Presentation on theme: "How to design and interpret controlled clinical trials “the dark side of the moon” “How to session” ESH June 2005 Andreas Pittaras MD."— Presentation transcript:

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