-
The use of a website, media, or advertisements to seek a positive effect. Use of a website, media or advertisements is a common recruitment strategy utilised in community-based trials. Our recruitment website was not initiated until the latter stages of the trial (June 2014, 2 years after study recruitment commenced), after which we recruited only 12 more participants. Of these, only one reported the website as their recruitment point. Use of a website, media or advertisements to deliberately and selectively seek a positive effect would have been a poor strategy; expectation bias that may have arisen from our recruitment materials would have affected both active and control conditions. While we were concerned about the possibility of expectation bias in those eventually randomised to the dietary condition, we were equally, if not more, concerned with the potential for contamination of the psychosocial support control condition—an evidence-based supported comparison of known benefit. It is well recognised that one of the main challenges in conducting lifestyle interventions relates to the fact that those in the control condition also often make changes and improvements to their lifestyles, based on the expectation of benefit [3]. As such, our recruitment materials would have been as least as likely to dilute the main effects of the intervention, creating a bias towards the null hypothesis.
-
The fruity smiley face (https://dietdepressionstudy.com/) and the local newspaper article to which Molendijk et al. [1] refer were from media interviews. The extensive observational literature in this field that predated and provided the rationale for the SMILES trial had already received very extensive coverage in both the Australian and international media. Thus, the idea that a healthy diet may be of benefit in patients with depression was widely understood by the public prior to the trial, and well before either that single article or our website. Three human research and ethics committees approved our study, including our media communications plans, materials and media interviews.
-
Molendijk et al. [1] query our primary outcome, the “interviewer-rated Montgomery–Åsberg Depression Rating Scale (MADRS)”. In fact, this is the gold-standard tool for assessing depressive symptoms in clinical trials and is the most widely used outcome measure. It is true that all subjective outcomes are sensitive to expectancy and hence may overestimate the effect. One of the acknowledged difficulties in psychiatry research is the lack of biomarkers or objective measures of mental health. As such, we are all restricted to the use of clinical assessments. This is a generic limitation of our trial and all others in the field. Including an active control with previous evidence of benefit is the best way to try and address this issue, and this is what we did. As reported in our original paper, all three mental health measures showed improvement in the diet group, relative to controls. We regard the correlation between changes in the modified Mediterranean diet score and MADRS in the intervention group as being consistent with a causal effect.
-
Loss of blinding in our study is a possibility and we agree that a loss of blinding will bias towards a bigger effect. However, we made considerable efforts to conceal group allocation from independent blind raters who were formally trained in the administration of the MADRS.
-
The dropout rate was higher in the befriending group, which may be a random finding, a marker of efficacy differential or a function of the trial design that is common to behavioural, psychological and lifestyle medicine trials. We confirm that we conducted thorough sensitivity analyses to examine the impact of non-random dropouts. The sensitivity analysis assumed dropouts were correlated with better outcomes in the control group and worse outcomes in the intervention group. Our findings withstood even extreme assumptions about the potential impact of non-random dropouts. Again, the nature of dropouts and potential biases were thoroughly addressed in our original manuscript. Additional file 1: Table S1 provides data on the characteristics of those who completed the follow-up and dropouts according to allocation groups.
Open Access 01.12.2018 | Correspondence
The SMILES trial: an important first step
Erschienen in: BMC Medicine | Ausgabe 1/2018