Health services in many countries increasingly rely on prescribed 'psychosocial interventions': treatments that use counselling techniques to tackle mental health issues, behavioural problems such as substance abuse, and assist parents with new or troubled children.

These highly-regarded therapeutic and educational programmes, devised by senior academics and practitioners, are sold commercially to public health services across the world on the basis that they are effective interventions for people in need of support - with the evidence to back them up.

However, the first study to investigate conflicts of interest in the published evidence for intervention treatments has revealed that the majority of academic studies which assert evidence of effectiveness list co-authors who profit from the distribution of these programmes, yet few declare a conflict of interest.

In fact, the new research shows that as many as two-thirds of the studies that list a co-author who financially benefits from sales of said treatment programmes declare no conflict of interest whatsoever.

While major steps have been taken to counter research bias in other fields such as pharmaceuticals, the new study's authors say that hugely influential psychosocial treatments suffer a distinct lack of transparency from academics that both publish research on treatment effectiveness and stand to gain significantly from any positive findings.

They write that as commercial psychosocial treatments - many of which cost hundreds, even thousands, of dollars per participant - continue to gain traction with national public health services, it is important that "systems for effective transparency are implemented" to ensure clinical commissioning bodies are aware of potential research biases. The findings are published in the journal PLOS ONE.

"Contrary to some, I have no problem with introducing commercial programmes into a national health service if decision makers and trusts come to the conclusion that a commercially disseminated treatment is more effective than their current psychosocial offerings, but this must be based on fair and transparent evidence," said the study's lead author Professor Manuel Eisner, from Cambridge's Institute of Criminology.

"What you don't want to see is an intervention system that remains as effective, or becomes less effective, despite buying in expensive programmes, because you have a public goods service competing with research that has a commercial interest to publish overly optimistic findings," Eisner said.

"Policy makers in public health have a right to expect transparency about conflicts of interest in academic research."

Four internationally disseminated psychosocial interventions - described by Eisner as "market leaders" - were examined: the Positive Parenting Programme (or Triple P); the Nurse-Family Partnership; the parenting and social skills programme Incredible Years; the Multi-Systemic Therapy intervention for youth offenders.

The researchers inspected all articles published in academic journals between 2008 and 2014 on these interventions that were co-authored by at least one lead developer of the programme - a total of 136 studies.

Two journal editors refused consent to be included in the research, leaving 134 studies. Of all these studies, researchers found 92 of them - equalling 71% - to have absent, incomplete or partly misleading conflict of interest disclosures.

The research team contacted journal editors about the 92 published studies on the effectiveness of one of these four commercial psychosocial interventions co-authored by a primary developer of the self-same therapy, yet listed no conflict of interest, or, in the case of a few, an incomplete one.

This led to 65 of the studies being amended with an 'erratum', or correction. In 16 cases, the journal editors admitted "mishandling" a disclosure, resulting in the lack of a conflict of interest statement.

In the remaining 49 cases, the journal editors contacted the study's authors seeking clarification. In every case the authors submitted a new or revised conflict of interest. Eisner and colleagues write that the "substantial variability in disclosure rates suggests that much responsibility seems to lie with the authors".

The most common reason given by those journals that did not issue a correction was that they did not have a conflict of interest policy in place at the time of the published study's submission.

While the overall rate of adequate disclosures in clear cases of conflict of interest was less than a third, just 32%, the rates for the four programmes varied significantly. The lowest rate of disclosures was found in academic studies on the Triple P programme, at just 11%.

Triple P is a standardised system of parenting support interventions based on cognitive-behavioural therapy. Initially developed by Professor Matthew Sanders at the University of Queensland, Triple P has sold around seven million copies of its standard programme across 25 countries since it began commercial operations in 1996, with over 62,000 licensed providers - mainly trained psychologists.

In 2001, Queensland 'spun out' the licencing contract into a private company, the royalties from which are distributed between three groups of beneficiaries: Queensland University itself, Prof Sanders' Parenting and Family Support Centre (also at Queensland), and the authors of Triple P.

Despite being one of the most widely evaluated parenting programmes worldwide, the evidence for the success of Triple P is controversial, say the researchers.

Several analyses of Triple P - including those by Triple P authors with previously undeclared conflicts of interest - show positive effects. However, at least one independent systematic review cited in the new PLOS ONE study found "no convincing evidence" that the Triple P has any positive effects in the long run.

"Researchers with a conflict of interest should not be presumed to conduct less valid scholarship, and transparency doesn't necessarily improve the quality of research, but it does make a difference to how those findings are assessed," said Eisner.

In the Journal of Child and Family Studies in January 2015, Triple P creator Prof Sanders wrote that "[p]artly as a result of these types of criticisms" his research group had "undertaken a comprehensive review of our own quality assurance practices".

Added Eisner: "The development of standardised, evidence-based programmes such as Triple P is absolutely the right thing to do. If we have comparable interventions providing an evidence base then it promotes innovation and stops us running around in circles. But we need to be able to trust the findings, and that requires transparency when it comes to conflicts of interest."