Title: A Central Storage Facility to Reduce Pesticide Suicides- A Feasibility Study from India

Transcription

1 Author's response to reviews Title: A Central Storage Facility to Reduce Pesticide Suicides- A Feasibility Study from India Authors: Lakshmi Vijayakumar (lakshmi@vijayakumars.com) Jeyaseelan Lakshmanan (lj@hotmail.com) Shuba Kumar (shubakumar@samarthngo.org) Rani Mohanraj (ranimohanraj@hotmail.com) Devika Shanmuga Sundaram (devika.cmc@gmail.com) Manikandan Sarojini (2manikandan@gmail.com) Version: 7 Date: 23 July 2013 Author's response to reviews: see over

2 From Dr. Lakshmi Kumar, Ph.D FRCPsch(Hony) Sneha & Voluntary Health Services No 11, Parkview Road, R.A.Puram Chennai To The Editor BMC Public Health Covering Letter Dear Editor, I am submitting the third revision to the manuscript of A Central Storage Facility to Reduce Pesticide Suicides- A Feasibility Study from India (Manuscript ID: MS: ) to your esteemed journal. I wish to thank the two reviewers for their comments and suggestions to the manuscript. We (the authors) have responded to the comments of the two reviewers which are presented below. Thanking you, Yours Sincerely, DR. Lakshmi Vijayakumar Title: A Central Storage Facility to Reduce Pesticide Suicides- A Feasibility Study from India 1

3 to Reviewer Comments to Reviewer Comments: Michael Eddleston Comment 1: This is a modestly improved paper in its revised form since so much more methodology is presented, clarifying the intervention and the study methodology. This is essential for a feasibility study. However, unfortunately, it has still not addressed my main concern that their findings are most likely simply due to chance and to the grossly imbalanced baseline rates of particularly pesticide self-harm in the two arms of the study. Although the title has been changed to indicate that it is a feasibility study, the results section remains the report of an intervention study. This is misleading. We have now rephrased the manuscript text suitably Comment 2: In the text itself, the authors write: Our study findings attest to the fact that, as a result of the central storage facility there was a statistically significant difference in the numbers of attempted and completed suicides between intervention and control sites. The storage facility had a protective effect in terms of minimizing suicides in the intervention sites. The reduction was 160 completed suicides and 135 attempted suicides by pesticide ingestion per 100,000 populations per year. The study cannot show this due to its small size and baseline differences. The abstract statement Demographic characteristics of individuals were similar across intervention and control sites is quite inadequate the incidence of the primary outcome was completely different at baseline. Thank you for your comments. Our sample size was decided upon objectively and we had clarified this in our earlier response to reviewer comments. Table 1 of our study data shows that there was an imbalance between intervention and control sites with respect to the variables, debts, income and pesticide usage. In order to adjust for these imbalances we carried out multi variable analysis ie. logistic regression for repeated measures (each patient coded as yes or no- binary outcome- taking each subject as a unit of analysis). This is Generalized Estimating Equation with binary outcomes. Here the repeated measures are pre (baseline) and post (follow up) measures. We needed to correlate this imbalance in relation to the outcome, namely suicide. Despite a higher percentage of these variables which are expected to be associated with higher rates of suicides, there was a larger reduction in suicides in the intervention sites as compared to the control sites This feasibility study has suggested the usefulness of the storage facility in reducing pesticide suicides.. 2

4 Regarding the sentence, Demographic characteristics of individuals were similar across intervention and control sites we appreciate your point and have removed this from the abstract. Comment 3: The effect seen may simply be regression to the mean, when two extreme baseline incidences simple settle back to the mean. As shown by table 3, there were ten pesticide suicides in the intervention arm and none in the control arm. After intervention, they both have the same number (2). It is most likely that the pre-intervention rated are artefacts, not that there was a change due to the intervention. We accept your concern about regression to the mean We need to have followed up for a longer period. However, we have adjusted baseline differences using multivariable analyses (GEE), where the baseline was considered as one time point. This also models the change and compares the change in intervention arm against the control arm. Comment 4: The baseline information was gained from a period of just 18 months. Perhaps an epidemic of fatal (and non-fatal) self-harm occurred in the intervention villages at some point during this time that was outside the normal? Perhaps the rates of fatal self-harm in the previous ten years were similar in the two areas and the postintervention period is just how it has always been? Unfortunately the study is too small and for too short a duration for any confident conclusions to be made. We appreciate your concern and understand that this is a limitation in our study. We are continuing with the intervention and will hopefully have better information in two years time. We have mentioned this as a limitation in the paper Comment 5: The abstract has to point out the grave imbalances in the primary outcome at baseline, before pointing out the changes in incidence. The limitations section of the paper has to be enlarged to explicitly deal with these problems. The results should talk about feasibility not effect and user views. We thank you for this advice. We have now revised the abstract incorporating the issues of baseline differences between intervention and control sites. We have also enlarged the limitation section in the paper highlighting these issues Comment: The abstract s initial conclusion: Conclusion: Suicide by pesticides poisoning is a major public health problem and needs innovative interventions to address it. This study, the first of its kind in the world, examined the feasibility of a central storage facility as a means of limiting access to pesticides. is accurate enough; however, it is quite discordant from the results section. The conclusion needs to include the baseline imbalances and a comment on feasibility and user perceptions 3

5 We thank you for pointing this out to us and as suggested have revised the conclusion suitably. to Reviewer Comments: Shu Sen Chang Major Compulsory Revisions Comment 1: In the results section of the abstract, the rate of change per year for overall pesticide suicides was should be something like the DIFFERENCE in the rate of change per year for overall pesticide suicides BETWEEN THE INTERVENTION AND CONTROL CITES was We thank you for this correction. This has been rephrased accordingly in the text Comment 2: I am not sure that Generalized Estimating Equation model is an appropriatestatistical approach here. The model may be used to compare the LEVELS OFSUICIDE RATES OVER TIME between the intervention and control villages, butthis is irrelevant to the primary outcome of interest, i.e. the DIFFERENCE INCHANGES BETWEEN PRE- AND POST-INTERVENTION SUICIDE RATES between the intervention and control villages. At some places in the manuscript logistic regression for repeated measure analysis was mentioned; this is confusing too, as the primary outcome is suicide rate, which is a continuous variable but not a binary variable. I feel if the authors are interested in presenting results adjusted for potential confounders they may consider linear regression models with the changes between pre- and postintervention suicide rates as the outcome variables, controlling for baseline differences in some important characteristics. Thank you for your comments. Our sample size was decided upon objectively which we had clarified in our earlier response to reviewer comments. Table 1 of our study data shows that there was an imbalance between intervention and control sites with respect to the variables, debts, income and pesticide usage. In order to adjust for these imbalances we carried out multi variable analysis ie. logistic regression for repeated measures (each patient coded as yes or no- binary outcome- taking each subject as a unit of analysis). This is Generalized Estimating Equation with binary outcomes. Here the repeated measures are pre (baseline) and post (follow-up) measures. We needed to correlate this imbalance in relation to the outcome, namely suicide. Despite a higher percentage of these variables which are expected to be associated with higher rates of suicides, there was a larger reduction in suicides in the intervention sites as compared to the control sites, This a feasibility study has suggested the usefulness of the storage facility in reducing pesticide suicides. 4

6 We appreciate your suggestion on linear regression model with rate of change as an outcome. Unfortunately we had only 4 sites with 4 variables plus a constant term to be modelled which is not possible for a linear model. The above analyses are more powerful, as we included each and every observation. Comment 3: I feel one important limitation that was not addressed by the authors, but pointed out by another reviewer, is the difference in baseline self-harm rates and other important community characteristics, and this is mainly due to the small size of the study. Although there is strong statistical evidence for the difference between arms, as shown in Tables 4 and 5, this may be due to the very high baseline rates in the intervention areas, which are likely to be associated with multiple factors such as greater level of deprivation and pesticide use. The difference in changes in suicide rates between arms may not be due to the intervention but result from regression to mean when both arms showed similar suicide rates towards the end of intervention. We appreciate your concern about the issue of regression to the mean and understand that this is a limitation in our study. We are continuing with the intervention and will hopefully have better information in two years time. This is a limitation which we have mentioned in the paper Comment 4: It s a bit unusual to report findings from focus group discussions in the discussion section (pages 16-18). The authors may consider including these in the Results section or simply dropping them. We agree with your suggestion but had included a few excerpts from the focus group discussions (FGD) based on the comments given by a reviewer the last time. We included it in the discussion section as we had not described the FGD methodology in detail. Hence we considered it inappropriate to present in the results section. Minor Essential Revisions Comment 1: Some statistics shown in Tables 4 and 5 were confusing. Rate / 100,000 was based on the denominator populations at baseline and follow-up respectively (i.e. per protocol ) whilst Change 1.5 year was based on the population at baseline only, in an ITT fashion. Therefore this would create some inconsistencies. For example, for attempted suicide in the intervention arm in Table 4, the difference between the baseline rate 359.9/100,000 and follow-up rate 69.6/100,000 was obviously not 292.4/100,000. Some footnotes may be needed here to clarify this and avoid confusions. 5

7 We thank you for these comments. The intention to treat (ITT) analyses included population at baseline as the denominator and per protocol (PP) analyses included population at follow up as the denominator. We have included appropriate foot notes for clarification. Comment 2: Gunnell et al 2007 BMC Public Health was cited when stating at least 275, ,000 suicides per year are by pesticide poisoning. This statistic is inflated compared to that reported in the original article, i.e. 233,997 to 325, There are typos at different places throughout the manuscript that need to be corrected, e.g. the government 084 [13] (page 4, the third line from the bottom). We thank you for pointing these errors out to us and apologise for them. We have now corrected these in the manuscript 6