PONE-D-19-17260

Snow avalanche deaths in Switzerland from 1995 to 2014 – results of a nation-wide linkage study

PLOS ONE

Dear Dr. Berlin,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Two reviewers with expertise in the field have evaluated your manuscript and provided very useful comments to build a stronger paper. Among these comments, please pay particular attention to (1) clarifying the segment presenting the statistical analysis, and how the  cohorts were built, (2) highlighting differences between individuals involved in skiing and those dying in avalanches, if possible, and how the linkage with the entire population might contribute to developing preventive measures, (3) removing or refining the distinction between voluntary and involuntary exposure.

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Reviewers' comments:

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Reviewer #1: Partly

Reviewer #2: Yes

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: I Don't Know

Reviewer #2: I Don't Know

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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5. Review Comments to the Author

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Reviewer #1: This paper tackles an important topic that has been poorly investigated until now, mostly because of methods constraints and difficulties.

In order to help direct prevention towards specific risk groups, the authors intend to provide detailed sociodemographic information about avalanche victims in Switzerland: do some sociodemographic factors impact exposure to avalanche mortality?

The originality of the approach lies in the linking of 2 databases: the "Snow and Avalanche Research" (SLF) which lists deaths caused by avalanches in Switzerland; the Swiss National Cohort (SNC) which reports the broader causes of mortality in Switzerland.

The authors highlight three main results.

The most interesting one is the connection revealed between avalanche victims’ places of residence and the locations of their fatal accidents. This is an important insight that should be developed further, in terms of interpretation, for the paper to provide a significant contribution.

The second result is the rate of 2 fatalities in avalanche for 1 million swiss residents each year. This information does not fit the research's objective and does not provide helpful information in terms of prevention, since it does not make it possible to estimate the risk exposure of actual mountain sports practitioners.

The third result is a very general profile of avalanche victims: mostly (young) men, with tertiary education, a privileged economic situation, living in an Alpine region. This result is not key since this merely echoes the profile of ski tourers and off-piste skiers. In other words, the methods used led to confirm that peoppe dying in avalanches are people involved in those dangerous activities, which is tautologic.

As a consequence, linking specific data (SLF) to global ones (SNC) does not prove relevant regarding the objective stated in the introduction: basing prevention on a more detailed picture of victims socio-demographics.

In order to get their paper published, the authors should address a couple of concerns, and acknowledge some limitations of their study:

- the methodological and scientific justification of the linkage between the databases must be explained more thoroughly. What does it make possible? What does it add to SLF data, in concrete terms? Currently, it is not celar why this linkage is useful and what limitation it makes it possibe to overcome.

- in the introduction, the authors state that « none of these studies allows a direct linkage between those recreating and those becoming a victim of an avalanche ». The problem is, broadening the scope to the swiss population does not help neither. By doing so, the authors don't focus on those recreating, which is the gap they identified in the literature. It must be made clearer why it helps to turn to general population data.

According to prevention experts, what is needed to enhance prevention is less a comparison with general population, than a better knowledge of the plural profiles of participants in the dangerous activities.

Beyond this central remark, some minor issues (easier to address) can be pointed out:

- the methods used by SLF to gather information regarding avalanches and avalanche victims must be precised. It will make it easier to understand if the data are precise and exhaustive. A better knowledge of such criteria would also help to understand the facts that are included or excluded in the data base

- what does « to be caught in an avalanche » mean? There are many envisageable outputs while an avalanche occurs: being swept away in the avalanche, and/or being buried in snow, and/or getting injured in tha avalanche, and/or being rescued (by specialized rescuers or members of the group), etc. This point is all the most crucial to address since it is further stated that 10% of the population that gets « caught » dies because of the avalanche. More precision is needed here.

- The authors write that « the activity of the accident party at the time of the avalanche event also was extracted » : is it always possible to identify the activity in question ? Especially when differentiating between off-piste skiing and ski touring: can we be positive on this distinction? What is it based on?

- « Persons voluntarily expose themselves to avalanche risk » : it seems more appropriate to replace voluntarily by knowingly

- Regarding the ICD-10 code X36: sometimes, while reporting the cause of deaths, physicians only use generic physiological terms. How can we be sure that this seemingly precise codification is properly used?

- « We speculate that persons with higher education, which often goes along with higher socioeconomic status and higher income, have more resources for leisure activities like ski-touring » : it seems simplistic to link a priviledged position, on an economical plan, and involvement in ski touring. The diffusion of this technical, distinctive activity is also, not to say mostly, a social and cultural process

- Some data from Switzerland or France highlight that over time, people dying in avalanche are older and older (from 37 to 42 for example, in France, in 25 or 30 years). This is a point that should be mentioned in the paper

- Last, avalanche safety equipment should be quantified; the reader actually needs a figure of equipment rate, and type of equipment. By the way, it seems that avalanche airbags are more commonly used in Switzerland than in Italy or France

Reviewer #2: This paper presents the most comprehensive review of Swiss avalanche fatality statistics to date and provides details of sociodemographic status and place of residence not previously reported. Additionally, larger trends of reduced fatalities in younger age groups over time is demonstrated raising some hope that avalanche safety technology and education may be successful.

The statistical analysis is complex and difficult to follow as currently written in the methods and results and clarification is needed. That being said, the discussion and conclusions follow logically from the stated objectives and the overall paper adds to the knowledge base regarding avalanche fatalities in Switzerland.

Line:

47- “still, 10%...die” needs reference.

72- Data regarding cause of avalanche death, time of burial, not relevant to study objective. Not reported in results or discussion. Eliminate.

76- One could argue that any skiing in mountainous terrain, “avalanche-secured” or otherwise, is a voluntary exposure to avalanches. Skiing is clearly a different exposure than occupying buildings or moving through transportation corridors. Your project does not address risk taking behavior specifically and voluntary/involuntary distinction as you describe does not change results. Would remove or re-word the voluntary/involuntary definitions.

91- add comma after nationality

96- SLF and SNC data linkage-

The statistical analysis and linkage is complex but the description of how and why two cohorts were developed (as shown in figure 2) does not follow from the methods. Was the 1995 census data extrapolated directly from the 1990 census? Why were two cohorts, 1990-2014 and 1995-2014, chosen? It seems that there is a significant overlap between the two cohorts. One would think that the Swiss population between 1990-2014, understanding influences from deaths and migration, is a single cohort. Overall the methods section needs to be clarified and the explanation simplified in regards to the time periods evaluated and then carried over with consistent time periods to the results.

108- would like to see a few examples of the expanded ICD9 codes.

142- “two regions defined by distance from the Alps…” Using the <=>25 km distinction adds little to the demographic data as you found a median distance of 61 km from residence to place of death and described victims as predominantly from an Alpine region. This would suggest that all of Switzerland is an Alpine region, which may be true. The 25 km measure offers little useful detail beyond just place of residence and location of death.

159- Table 1. Two time periods 1/1/1995-2000 and 5/12/1995-2014 are given but it is not clear why or how these two periods were chosen. See above for line 96, there is a lack of clarity on how cohorts and time periods were determined. You also list “time periods” in line 160 then report in line 172-3 “two points in time”, both for same table. This is confusing.

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Reviewer #1: No

Reviewer #2: No

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Snow avalanche deaths in Switzerland from 1995 to 2014 – results of a nation-wide linkage study

PONE-D-19-17260R1

Dear Dr. Berlin,

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With kind regards,

Bruno Masquelier, PhD

Academic Editor

PLOS ONE

Additional Editor Comments (optional): All questions and comments from the reviewers have been addressed. Thank you.

Reviewers' comments: