Multiple flaws pose more threats to the validity of psychotherapy studies than would be inferred when the individual flaws are considered independently.
We can learn to spot features of psychotherapy trials that are likely to lead to exaggerated claims of efficacy for treatments or claims that will not generalize beyond the sample that is being studied in a particular clinical trial. We can look to the adequacy of sample size, and spot what Cochrane collaboration has defined as risk of bias in their handy assessment tool.
We can look at the case-mix in the particular sites where patients were recruited. We can examine the adequacy of diagnostic criteria that were used for entering patients to a trial. We can examine how blinded the trial was in terms of whoever assigned patients to particular conditions, but also what the patients, the treatment providers, and their evaluaters knew which condition to which particular patients were assigned.
And so on. But what about combinations of these factors?
We typically do not pay enough attention multiple flaws in the same trial. I include myself among the guilty. We may suspect that flaws are seldom simply additive in their effect, but we don’t consider whether they may be even synergism in the negative effects on the validity of a trial. As we will see in this analysis of a clinical trial, multiple flaws can provide more threats to the validity trial than what we might infer when the individual flaws are considered independently.
The particular paper we are probing is described in its discussion section as the “largest RCT to date testing the efficacy of group CBT for patients with CFS.” It also takes on added importance because two of the authors, Gijs Bleijenberg and Hans Knoop, are considered leading experts in the Netherlands. The treatment protocol was developed over time by the Dutch Expert Centre for Chronic Fatigue (NKCV, http://www.nkcv.nl; Knoop and Bleijenberg, 2010). Moreover, these senior authors dismiss any criticism and even ridicule critics. This study is cited as support for their overall assessment of their own work. Gijs Bleijenberg claims:
Cognitive behavioural therapy is still an effective treatment, even the preferential treatment for chronic fatigue syndrome.
“Not everybody endorses these conclusions, however their objections are mostly baseless.”
This is a long read blog post. I will offer a summary for those who don’t want to read through it, but who still want the gist of what I will be saying. However, as always, I encourage readers to be skeptical of what I say and to look to my evidence and arguments and decide for themselves.
Authors of this trial stacked the deck to demonstrate that their treatment is effective. They are striving to support the extraordinary claim that group cognitive behavior therapy fosters not only better adaptation, but actually recovery from what is internationally considered a physical condition.
There are some obvious features of the study that contribute to the likelihood of a positive effect, but these features need to be considered collectively, in combination, to appreciate the strength of this effort to guarantee positive results.
This study represents the perfect storm of design features that operate synergistically:
Referral bias – Trial conducted in a single specialized treatment setting known for advocating psychological factors maintaining physical illness.
Strong self-selection bias of a minority of patients enrolling in the trial seeking a treatment they otherwise cannot get.
Broad, overinclusive diagnostic criteria for entry into the trial.
Active treatment condition carry strong message how patients should respond to outcome assessment with improvement.
An unblinded trial with a waitlist control lacking the nonspecific elements (placebo) that confound the active treatment.
Subjective self-report outcomes.
Specifying a clinically significant improvement that required only that a primary outcome be less than needed for entry into the trial
Deliberate exclusion of relevant objective outcomes.
Avoidance of any recording of negative effects.
Despite the prestige attached to this trial in Europe, the US Agency for Healthcare Research and Quality (AHRQ) excludes this trial from providing evidence for its database of treatments for chronic fatigue syndrome/myalgic encephalomyelitis. We will see why in this post.
The take away message: Although not many psychotherapy trials incorporate all of these factors, most trials have some. We should be more sensitive to when multiple factors occur in the same trial, like bias in the site for patient recruitment; lacking of blinding; lack of balance between active treatment and control condition in terms of nonspecific factors, and subjective self-report measures.
The article reporting the trial is
Wiborg JF, van Bussel J, van Dijk A, Bleijenberg G, Knoop H. Randomised controlled trial of cognitive behaviour therapy delivered in groups of patients with chronic fatigue syndrome. Psychotherapy and Psychosomatics. 2015;84(6):368-76.
Unfortunately, the article is currently behind a pay wall. Perhaps readers could contact the corresponding author Hans.email@example.com and request a PDF.
Background: Meta-analyses have been inconclusive about the efficacy of cognitive behaviour therapies (CBTs) delivered in groups of patients with chronic fatigue syndrome (CFS) due to a lack of adequate studies. Methods: We conducted a pragmatic randomised controlled trial with 204 adult CFS patients from our routine clinical practice who were willing to receive group therapy. Patients were equally allocated to therapy groups of 8 patients and 2 therapists, 4 patients and 1 therapist or a waiting list control condition. Primary analysis was based on the intention-to-treat principle and compared the intervention group (n = 136) with the waiting list condition (n = 68). The study was open label. Results: Thirty-four (17%) patients were lost to follow-up during the course of the trial. Missing data were imputed using mean proportions of improvement based on the outcome scores of similar patients with a second assessment. Large and significant improvement in favour of the intervention group was found on fatigue severity (effect size = 1.1) and overall impairment (effect size = 0.9) at the second assessment. Physical functioning and psychological distress improved moderately (effect size = 0.5). Treatment effects remained significant in sensitivity and per-protocol analyses. Subgroup analysis revealed that the effects of the intervention also remained significant when both group sizes (i.e. 4 and 8 patients) were compared separately with the waiting list condition. Conclusions: CBT can be effectively delivered in groups of CFS patients. Group size does not seem to affect the general efficacy of the intervention which is of importance for settings in which large treatment groups are not feasible due to limited referral
The trial registration
Who was enrolled into the trial?
Who gets into a psychotherapy trial is a function of the particular treatment setting of the study, the diagnostic criteria for entry, and patient preferences for getting their care through a trial, rather than what is being routinely provided in that setting.
We need to pay particular attention to when patients enter psychotherapy trials hoping they will receive a treatment they prefer and not to be assigned to the other condition. Patients may be in a clinical trial for the betterment of science, but in some settings, they are willing to enroll because of a probability of getting treatment they otherwise could not get. This in turn also affects the evaluation of both the condition in which they get the preferred treatment, but also their evaluation of the condition in which they are denied it. Simply put, they register being pleased with what they wanted or not being pleased if they did not get what they wanted.
The setting is relevant to evaluating who was enrolled in a trial.
The authors’ own outpatient clinic at the Radboud University Medical Center was the site of the study. The group has an international reputation for promoting the biopsychosocial model, in which psychological factors are assumed to be the decisive factor in maintaining somatic complaints.
All patients were referred to our outpatient clinic for the management of chronic fatigue.
There is thus a clear referral bias or case-mix bias but we are not provided a ready basis for quantifying it or even estimating its effects.
The diagnostic criteria.
The article states:
In accordance with the US Center for Disease Control , CFS was defined as severe and unexplained fatigue which lasts for at least 6 months and which is accompanied by substantial impairment in functioning and 4 or more additional complaints such as pain or concentration problems.
Actually, the US Center for Disease Control would now reject this trial because these entry criteria are considered obsolete, overinclusive, and not sufficiently exclusive of other conditions that might be associated with chronic fatigue.*
There is a real paradigm shift happening in America. Both the 2015 IOM Report and the Centers for Disease Control and Prevention (CDC) website emphasize Post Exertional Malaise and getting more ill after any effort with M.E. CBT is no longer recommended by the CDC as treatment.
The only mandatory symptom for inclusion in this study is fatigue lasting 6 months. Most properly, this trial targets chronic fatigue [period] and not the condition, chronic fatigue syndrome.
Current US CDC recommendations (See box 7-1 from the IoM document, above) for diagnosis require postexertional malaise for a diagnosis of myalgic encephalomyelitis (ME). See below.
Patients meeting the current American criteria for ME would be eligible for enrollment in this trial, but it’s unclear what proportion of the patients enrolled actually met the American criteria. Because of the over-inclusiveness of the entry diagnostic criteria, it is doubtful whether the results would generalize to American sample. A look at patient flow into the study will be informative.
Let’s look at what is said in the text, but also in the chart depicting patient flow into the trial for any self-selection that might be revealed.
In total, 485 adult patients were diagnosed with CFS during the inclusion period at our clinic (fig. 1). One hundred and fifty-seven patients were excluded from the trial because they declined treatment at our clinic, were already asked to participate in research incompatible with inclusion (e.g. research focusing on individual CBT for CFS) or had a clinical reason for exclusion (i.e. they received specifically tailored interventions because they were already unsuccessfully treated with individual CBT for CFS outside our clinic or were between 18 and 21 years of age and the family had to be involved in the therapy). Of the 328 patients who were asked to engage in group therapy, 99 (30%) patients indicated that they were unwilling to receive group therapy. In 25 patients, the reason for refusal was not recorded. Two hundred and four patients were randomly allocated to one of the three trial conditions. Baseline characteristics of the study sample are presented in table 1. In total, 34 (17%) patients were lost to follow-up. Of the remaining 170 patients, 1 patient had incomplete primary outcome data and 6 patients had incomplete secondary outcome data.
We see that the investigators invited two thirds of patients attending the clinic to enroll in the trial. Of these, 41% refused. We don’t know the reason for some of the refusals, but almost a third of the patients approached declined because they did not want group therapy. The authors left being able to randomize 42% of patients coming to the clinic or less than two thirds of patients they actually asked. Of these patients, a little more than two thirds received the treatment to which were randomized and were available for follow-up.
These patients receiving treatment to which they were randomized and who were available for follow-up are self-selected minority of the patients coming to the clinic. This self-selection process likely reduced the proportion of patients with myalgic encephalomyelitis. It is estimated that 25% of patients meeting the American criteria a housebound and 75% are unable to work. It’s reasonably to infer that patients being the full criteria would opt out of a treatment that require regular attendance of a group session.
The trial is biased to ambulatory patients with fatigue and not ME. Their fatigue is likely due to some combinations of factors such as multiple co-morbidities, as-yet-undiagnosed medical conditions, drug interactions, and the common mild and subsyndromal anxiety and depressive symptoms that characterize primary care populations.
The treatment being evaluated
Group cognitive behavior therapy for chronic fatigue syndrome, either delivered in a small (4 patients and 1 therapist) or larger (8 patients and 2 therapists) group format.
The intervention consisted of 14 group sessions of 2 h within a period of 6 months followed by a second assessment. Before the intervention started, patients were introduced to their group therapist in an individual session. The intervention was based on previous work of our research group [4,13] and included personal goal setting, fixing sleep-wake cycles, reducing the focus on bodily symptoms, a systematic challenge of fatigue-related beliefs, regulation and gradual increase in activities, and accomplishment of personal goals. A formal exercise programme was not part of the intervention.
Patients received a workbook with the content of the therapy. During sessions, patients were explicitly invited to give feedback about fatigue-related cognitions and behaviours to fellow patients. This aspect was introduced to facilitate a pro-active attitude and to avoid misperceptions of the sessions as support group meetings which have been shown to be insufficient for the treatment of CFS.
In contrast to our previous work , we communicated recovery in terms of fatigue and disabilities as general goal of the intervention.
Some impressions of the intensity of this treatment. This is a rather intensive treatment with patients having considerable opportunities for interactions with providers. This factor alone distinguishes being assigned to the intervention group versus being left in the wait list control group and could prove powerful. It will be difficult to distinguish intensity of contact from any content or active ingredients of the therapy.
I’ll leave for another time a fuller discussion of the extent to which what was labeled as cognitive behavior therapy in this study is consistent with cognitive therapy as practiced by Aaron Beck and other leaders of the field. However, a few comments are warranted. What is offered in this trial does not sound like cognitive therapy as Americans practice it. What is often in this trial seems emphasize challenging beliefs, pushing patients to get more active, along with psychoeducational activities. I don’t see indications of the supportive, collaborative relationship in which patients are encouraged to work on what they want to work on, engage in outside activities (homework assignments) and get feedback.
What is missing in this treatment is what Beck calls collaborative empiricism, “a systemic process of therapist and patient working together to establish common goals in treatment, has been found to be one of the primary change agents in cognitive-behavioral therapy (CBT).”
Importantly, in Beck’s approach, the therapist does not assume cognitive distortions on the part of the patient. Rather, in collaboration with the patient, the therapist introduces alternatives to the interpretations that the patient has been making and encourages the patient to consider the difference. In contrast, rather than eliciting goal statements from patients, therapist in this study imposes the goal of increased activity. Therapists in this study also seem ready to impose their views that the patients’ fatigue-related beliefs are maladaptive.
The treatment offered in this trial is complex, with multiple components making multiple assumptions that seem quite different from what is called cognitive therapy or cognitive behavioral therapy in the US.
The authors’ communication of recovery from fatigue and disability seems a radical departure not only from cognitive behavior therapy for anxiety and depression and pain, but for cognitive behavior therapy offered for adaptation to acute and chronic physical illnesses. We will return to this “communication” later.
The control group
Patients not randomized to group CBT were placed on a waiting list.
Think about it! What do patients think about having gotten involved in all the inconvenience and burden of a clinical trial in hope that they would get treatment and then being assigned to the control group with just waiting? Not only are they going to be disappointed and register that in their subjective evaluations of the outcome assessments patients may worry about jeopardizing the right to the treatment they are waiting for if they overly endorse positive outcomes. There is a potential for nocebo effect , compounding the placebo effect of assignment to the CBT active treatment groups.
What are informative comparisons between active treatments and control conditions?
We need to ask more often what inclusion of a control group accomplishes for the evaluation of a psychotherapy. In doing so, we need to keep in mind that psychotherapies do not have effect sizes, only comparisons of psychotherapies and control condition have effect sizes.
A pre-post evaluation of psychotherapy from baseline to follow-up includes the effects of any active ingredient in the psychotherapy, a host of nonspecific (placebo) factors, and any changes that would’ve occurred in the absence of the intervention. These include regression to the mean– patients are more likely to enter a clinical trial now, rather than later or previously, if there has been exacerbation of their symptoms.
So, a proper comparison/control condition includes everything that the patients randomized to the intervention group get except for the active treatment. Ideally, the intervention and the comparison/control group are equivalent on all these factors, except the active ingredient of the intervention.
That is clearly not what is happening in this trial. Patients randomized to the intervention group get the intervention, the added intensity and frequency of contact with professionals that the intervention provides, and all the support that goes with it; and the positive expectations that come with getting a therapy that they wanted.
Attempts to evaluate the group CBT versus the wait-list control group involved confounding the active ingredients of the CBT and all these nonspecific effects. The deck is clearly being stacked in favor of CBT.
This may be a randomized trial, but properly speaking, this is not a randomized controlled trial, because the comparison group does not control for nonspecific factors, which are imbalanced.
The unblinded nature of the trial
In RCTs of psychotropic drugs, the ideal is to compare the psychotropic drug to an inert pill placebo with providers, patients, and evaluate being blinded as to whether the patients received psychotropic drug or the comparison pill.
While it is difficult to achieve a comparable level of blindness and a psychotherapy trial, more of an effort to achieve blindness is desirable. For instance, in this trial, the authors took pains to distinguish the CBT from what would’ve happened in a support group. A much more adequate comparison would therefore be CBT versus either a professional or peer-led support group with equivalent amounts of contact time. Further blinding would be possible if patients were told only two forms of group therapy were being compared. If that was the information available to patients contemplating consenting to the trial, it wouldn’t have been so obvious from the outset to the patients being randomly assigned that one group was preferable to the other.
Subjective self-report outcomes.
The primary outcomes for the trial were the fatigue subscale of the Checklist Individual Strength; the physical functioning subscale of the Short Health Survey 36 (SF-36); and overall impairment as measured by the Sickness Impact Profile (SIP).
Realistically, self-report outcomes are often all that is available in many psychotherapy trials. Commonly these are self-report assessments of anxiety and depressive symptoms, although these may be supplemented by interviewer-based assessments. We don’t have objective biomarkers with which to evaluate psychotherapy.
These three self-report measures are relatively nonspecific, particularly in a population that is not characterized by ME. Self-reported fatigue in a primary care population lacks discriminative validity with respect to pain, anxiety and depressive symptoms, and general demoralization. The measures are susceptible to receipt of support and re-moralization, as well as gratitude for obtaining a treatment that was sought.
Self-report entry criteria include a score 35 or higher on the fatigue severity subscale. Yet, a score of less than 35 on this scale at follow up is part of what is defined as a clinically significant improvement with a composite score from combined self-report measures.
We know from medical trials that differences can be observed with subjective self-report measures that will not be found with objective measures. Thus, mildly asthmatic patients will fail to distinguish in their subjective self-reports between [ between the effective inhalant albuterol, an inert inhalant, and sham acupuncture, but will rate improvement better than getting no intervention. However, there will be a strong advantage over the other three conditions with an objective measure, maximum forced expiratory volume in 1 second (FEV1) as assessed with spirometry.
The suppression of objective outcome measures
We cannot let these the authors of this trial off the hook in their dependence on subjective self-report outcomes. They are instructing patients that recovery is the goal, which implies that it is an attainable goal. We can reasonably be skeptical about acclaim of recovery based on changes in self-report measures. Were the patients actually able to exercise? What was their exercise capacity, as objectively measured? Did they return to work?
These authors have included such objective measurements in past studies, but not included them as primary outcomes, nor, even in some cases, reported them in the main paper reporting the trial.
Wiborg JF, Knoop H, Stulemeijer M, Prins JB, Bleijenberg G. How does cognitive behaviour therapy reduce fatigue in patients with chronic fatigue syndrome? The role of physical activity. Psychol Med. 2010 Jan 5:1
The senior authors’ review fails to mention their three studies using actigraphy that did not find effects for CBT. I am unaware of any studies that did find enduring effects.
Perhaps this is what they mean when they say the protocol has been developed over time – they removed what they found to be threats to the findings that they wanted to claim.
Dismissing of any need to consider negative effects of treatment
Most psychotherapy fail to assess any adverse effects of treatment, but this is usually done discretely, without mention. In contrast, this article states
Potential harms of the intervention were not assessed. Previous research has shown that cognitive behavioural interventions for CFS are safe and unlikely to produce detrimental effects.
Patients who meet stringent criteria for ME would be put at risk for pressure to exert themselves. By definition they are vulnerable to postexertional malaise (PEM). Any trail of this nature needs to assess that risk. Maybe no adverse effects would be found. If that were so, it would strongly indicate the absence of patients with appropriate diagnoses.
Timing of assessment of outcomes varied between intervention and control group.
I at first did not believe what I was reading when I encountered this statement in the results section.
The mean time between baseline and second assessment was 6.2 months (SD = 0.9) in the control condition and 12.0 months (SD = 2.4) in the intervention group. This difference in assessment duration was significant (p < 0.001) and was mainly due to the fact that the start of the therapy groups had to be frequently postponed because of an irregular patient flow and limited treatment capacities for group therapy at our clinic. In accordance with the treatment manual, the second assessment was postponed until the fourteenth group session was accomplished. The mean time between the last group session and the second assessment was 3.3 weeks (SD = 3.5).
So, outcomes were assessed for the intervention group shortly after completion of therapy, when nonspecific (placebo) effects would be stronger, but a mean of six months later than for patients assigned to the control condition.
Post-hoc statistical controls are not sufficient to rescue the study from this important group difference, and it compounds other problems in the study.
Take away lessons
Pay more attention to how limitations any clinical trial may compound each other in terms of the trial provide exaggerated estimates of the effects of treatment or the generalizability of the results to other settings.
Be careful of loose diagnostic criteria because a trial may not generalize to the same criteria being applied in settings that are different either in terms of patient population of the availability of different treatments. This is particularly important when a treatment setting has a bias in referrals and only a minority of patients being invited to participate in the trial actually agree and are enrolled.
Ask questions about just what information is obtained in comparing active treatment group and the study to its control/comparison. For start, just what is being controlled and how might that affect the estimates of the effectiveness of the active treatment?
Pay particular attention to the potent combination of the trial being unblinded, a weak comparision/control, and an active treatment that is not otherwise available to patients.
*The means of determining whether the six months of fatigue might be accounted for by other medical factors was specific to the setting. Note that a review of medical records for sufficient for an unknown proportion of patients, with no further examination or medical tests.
The Department of Internal Medicine at the Radboud University Medical Center assessed the medical examination status of all patients and decided whether patients had been sufficiently examined by a medical doctor to rule out relevant medical explanations for the complaints. If patients had not been sufficiently examined, they were seen for standard medical tests at the Department of Internal Medicine prior to referral to our outpatient clinic. In accordance with recommendations by the Centers for Disease Control, sufficient medical examination included evaluation of somatic parameters that may provide evidence for a plausible somatic explanation for prolonged fatigue [for a list, see . When abnormalities were detected in these tests, additional tests were made based on the judgement of the clinician of the Department of Internal Medicine who ultimately decided about the appropriateness of referral to our clinic. Trained therapists at our clinic ruled out psychiatric comorbidity as potential explanation for the complaints in unstructured clinical interviews.