Author s response to reviews

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1 Author s response to reviews Title: Mortality patterns and risk among older men and women with intellectual disability: a Swedish national retrospective cohort study Authors: Nawi Ng (nawi.ng@umu.se) Eva Flygare Wallén (eva.flygare.wallen@ki.se) Gerd Ahlström (gerd.ahlstrom@med.lu.se) Version: 1 Date: 03 Oct 2017 Author s response to reviews: Letter to Editor Dear Editor, We would like to express our gratitude for your positive response and constructive reviewers comments for our manuscript. We are glad to know that you would consider our manuscript for publication in BMC Geriatrics, pending the revisions suggested by the reviewers. Please kindly find our response to the editor s and reviewers comments. We have made our best efforts to address the reviewers concerns and we think that our manuscript is much stronger following the revision. We look forward to hearing from you. Warm regards, Nawi Ng, Eva Flygare Wallén and Gerd Ahlström

2 . Response to Reviewers Comments BGTC-D Mortality patterns and risk among older men and women with intellectual disability: a Swedish national retrospective cohort study Nawi Ng, MD, MPH, PhD; Eva Flygare Wallén, RN, PhD; Gerd Ahlström, Ph.D. BMC Geriatrics We thank the editor and the two reviewers for their positive and constructive comments which are very helpful for us in revising and improving the quality of our paper. We have made our best efforts to address the reviewers concerns and we think that our manuscript is much stronger in its current form. We have also ensured the completeness of the Declaration section at the end of the manuscript. Please find our point-to-point response to the reviewers comments. Reviewer reports: Marsha Mailick (Reviewer 1) Reviewer s comment: This manuscript addresses an important topic - namely rates of mortality and causes of death among individuals with intellectual disability in Sweden. The data suggest higher rates of mortality, earlier ages at death, and different causes of death within this population, consistent with other studies in different countries. Authors response: We thank Prof. Marsha Mailick for her appreciation to our study. While studies on mortality among children with intellectual disabilities are abundant, research on mortality among older people with intellectual disabilities, especially in Sweden, are quite scarce. Our study fills in these gaps of knowledge. Reviewer s comment: Yet there were some inconsistencies across studies about the most prominent causes of death in the ID population, and it would have been helpful to explore whether these differences were due in part to methodological differences in definitions, sources of data, or other aspects of the research design. This important consideration was mentioned (page 3, line 93-94), but the paper warrants greater analysis of past research. Authors response: We fully agree with Prof. Mailick that analysis of past research on the causes of death among population with intellectual disabilities is very relevant, considering the multitude research results reported by researchers. Using the keywords intellectual disabilities

3 AND cause of death, we identified only one systematic review paper looking into mortality among children with autism spectrum disorder. No systematic review and/or meta-analysis on the cause of death among older population with intellectual disabilities exist. This is certainly an interesting research question to investigate, which unfortunately is out of the scope of this paper. We have added a few sentences in the Strength within the Discussion section to accommodate Prof. Mailick s suggestion. This study fills in the gap of knowledge on cause-of-death among older people with intellectual disabilities, and considering the growing number of evidence on this field, a systematic review and/or meta-analysis on cause-of-death patterns among older people with intellectual disabilities is warranted. Reviewer s comment: Although the literature cited is comprehensive, at least one relevant population-based US study is not included, namely Maenner at al. (2015) in the American Journal of Intellectual and Developmental Disabilities. Authors response: We thank Prof. Mailick for pointing out this important reference. We have now included the citation to this reference in the Discussion section as Reference 29. Reviewer s comment: As a rationale for the present study, it is noted that the closure of institutions in Sweden may result in changes in care across the life span and that the data analyzed here represent the first opportunity to study a post-institutional context of care for the population with ID. The paper would have been strengthened with the inclusion of data about prior institutionalization and residential history of participants, as these factors have been shown to affect access to health care and exposure to disease. If the sources of data used in the present study may not have included residential history information, this limits the extent to which inferences can be drawn about the post-institutional mortality in the population with ID. Authors response: We fully agree with Prof. Mailick on the importance to control for residential history information in the analysis as it might affect exposure to disease, access to health care and subsequently the mortality. In Sweden, no register covering the adult age for the cohort of older people in our study exists. Such registration was forbidden considering what happened to people with intellectual disability before or during the World War II Period. We have now added this as a limitation of our study. As the LSS data is only available from 2007 (the register started in 2004 with very limited data) and no earlier register of individuals with ID exists, it is not possible for us to control for prior

4 institutionalisation among the individuals with ID before the closure of care institutions in the 70s. In Sweden, no register covering the adult age for the cohort of older people in our study exists. Such registration was forbidden considering what happened to people with intellectual disability before or during the World War II Period. The establishment of the LSS law and the LSS register in 2004 was a breakthrough in understanding the health patterns and health care needs among people with intellectual disability in Sweden. Therefore, the results of this study should be interpreted in light of other potential confounding factors such as residential history, prior institutionalization, access to health care, exposure to different factors, as well as life-style behaviours which might influence the outcome of this study the mortality. Similarly, as these data are not available in our study, we cannot explain whether the differential mortality level observed among individuals with ID and the general population were due to biological differences or the effects of the above-mentioned confounding factors. Reviewer s comment: The inclusion of individuals with ICD-10 codes of disorders of psychological development can be questioned. Authors response: As we described in the Methods/ Identification of individuals in datasets section, we included the diagnosis categories: mental retardation (F70 73, F78 79), disorders of psychological development (F84, F88 89) and DS (Q90). Based on the available expertise in this field in our research group, we included individuals with diagnoses entitled to receive support according to the LSS law. Reviewer s comment: The fundamental question motivating research on mortality in individuals with ID is whether differences in mortality as compared with the general population are due to biological differences, differences in health care access and utilization, or differences in exposures. The present study does not address this fundamental question. Authors response: We thank Prof. Mailick for this comment. We have now added this in the limitation of the study. As the LSS data is only available from 2007 and no earlier register of individuals with ID exists, it is not possible for us to control for prior institutionalisation among the individuals with ID before the closure of care institutions in the 70s. Therefore, the results of this study should be interpreted in light of other potential confounding factors such as residential history, prior institutionalization, access to health care, exposure to different factors, as well as life-style behaviours which might influence the outcome of this study the mortality. Similarly, as these data are not available in our study, we cannot explain whether the differential mortality level

5 observed among individuals with ID and the general population were due to biological differences or the effects of the above-mentioned confounding factors. Reviewer reports: Shu-Fang Chang (Reviewer 2) This is an important and interesting top about "Mortality patterns and risk among older men and women with intellectual disability". Based on the purpose of the study, authors clearly state the findings and discussion. I have no further suggestions. Authors response: We appreciate the positive appreciation of Dr. Chang to our study. We hope that this study can contribute to fill the gaps in this study area.