@2024 Afarand., IRAN

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ISSN: 2008-2630    Iranian Journal of War & Public Health 2015;7(3):123-125

Background
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Previous Studies
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Aim(s)
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Research type
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Research society, place and time
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Sampling method and number
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Used devices&materials
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Findings by Text
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Main comparison to the similar studies
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Suggestions
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Limitations
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Conclusions
Based on an article entitled as “comment on incidence of cancer in Iranian sulfur mustard (SM) exposed veterans” [1] published in Inhalation Toxicology journal, there are some comments on “incidence of cancer in Iranian sulfur mustard exposed veterans: a long-term follow-up cohort study” [2]. Then it is needed to respond to the comments. • “The type of the study is more a historical cohort; since instead of the identification of the group members simultaneously, the members have been identified based on the former history of exposure. In addition, the cases should be followed up for a long period in the author’s plan.” [1] A cohort study can be done by going back in time to comprise the cohorts and following them up to the present (retrospective cohort study) or alternatively, by going ahead in time from the present (prospective cohort study) [3]. Since this study is both a combination of retrospective and prospective (10 years before and 10 years after), it can be concluded that the type of this study is ambidirectional cohort other than a historical [4].Moreover, the study still continues as declared in the paper. • The author asked "Why the authors did not control the effect of some more important variables such as exposure episodes, and the use of gas masks that are available for veterans' health records?" [1]. We could not control the effects of some important variables related to the exposure including using protective equipment, dose and level of exposure in the study [2]. In fact, there was not a reliable method to record the level of SM-exposure, and due to the high probability of recall bias we did not collect this data. • “In order to compute the ratio of cancer risk in SM-exposed group, Cox proportional hazards model has been used. Based on the model, it is assumed that the ratio of the risk of the predicting variables is constant in time, i. e. the risk of one person is proportional to other persons and there is no time-dependent variable. Nevertheless, if the time-dependent variables should be assumed, Cox proportional hazards model might be improper to assess data and extended Cox model should be used. Since most of the studied variables, such as smoking, educational level, and age, are time-dependent variables, why extended Cox model has not been used by the authors?” [1] To investigate the presuppositions of Cox proportional hazards model, “graphical test of risks constant over time” might be used [5]. Since in the main study, Cox proportional hazards model has been valid for the proportion assumptions, the model has been used to compute the ratio of cancer in SM-exposed group instead of extended Cox model. • There is a difference between the findings of the total ratio of cancer and the ratio in the subgroups. “Since cancer is composed of all the subgroups, how the difference is explained by the authors?” [1] There was a difference between the total cancer findings and the findings in the subgroups without any present explanation. However, it might be explained by the next findings of cohort study. • Despite the fact that the incidence rate of cancer did not differ between groups (SM exposed and non-exposed), but carcinogenicity of SM has been introduced by the authors [1]. Based on the significantly higher incidence rate of cancer in SM-exposed veterans comparing to unexposed (p<0.001), authors suggested carcinogenicity of SM [2]. There was no significant difference between the groups in the cancer type. Therefore, it was not possible to signify what cancer had been related to SM-exposure at the study step. Following the cases is the only way to find which cancer is higher in SM-exposed veterans.
Acknowledgments
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Conflict of interest
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Ethical Permissions
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Funding Sources
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