Primary and
hospital care
The Swiss army knife impact study: a survival analysis
Restez vigilants lorsqu’une étude présente des corrélations surprenantes ...

The Swiss army knife impact study: a survival analysis

Lehren und Forschen
Isabelle Jacot Sadowski
Autres auteurs
Daniel Widmer, Philippe Staeger, Prof. Dr méd PhD Nicolas Senn, Kevin Selby, Sylvie Payot, Anne Niquille, Alexandra N'Goran, David Nanchen, Laurance Kerboas, The Swiss knife working group:, Lilli Herzig, Bernard Favrat, Sonja T. Ebert, Serge de Vallière, Anouk Deruaz Luyet, Christine Cohidon, Carole Clair, Patrick Bodenmann, Reto Auer
Édition
2018/04
DOI:
https://doi.org/10.4414/phc-f.2018.01697
Prim Hosp Care (fr). 2018;18(04):64-65
Data Supplement
TheSwissarmyknifeimpactstudy_longversion.pdf
Affiliations
Pour le working group: Policlinique Médicale Universitaire, Lausanne

Publié le 21.02.2018

Introduction

Life expectancy varies substantially among countries and is influenced by many factors. The Swiss army knife, a brilliant tool that was designed to improve living conditions and potentially to aid survival in challenging environments, might be associated with increased life expectancy. In this study we aimed to assess the relationship between life expectancy and rates of Swiss army knife purchase, a surrogate of the use of multi-utility Swiss army knives (MUSK), at a ­population level.

Method

This was an ecological study assessing the association between the purchase of Swiss army knives and healthy life expectancy. To take into account socio­economic status, data for low income and high income countries were analysed separately. Data for Switzerland were corrected to represent the number of MUSK sold to Swiss citizens only (2.1% of the total MUSK sold in the country).

Main results

Data from 41 countries were retrieved from the Swiss army knife manufacturer. A strong and linear association was found between rate of purchase of Swiss army knives and life expectancy (r = 0.43, p <0.05). Graphical assessment identified one outlier country (Germany) so this outlier was eliminated from the subsequent analyses (fig. 1).
A positive association was also found in ­analyses stratified for high and low income countries (β = 0.11, p = 0.043 and β = 1.81, p = 0.009, respectively). The life expectancy of the population increased by a healthy year for every 0.6 and 9.1 Swiss army knives purchased per 10 000 inhabitants in high and low income countries, respectively.
Figure 1: Correlation between multi-utility Swiss army knives and healthy life expectancy (without Germany; corrected for Switzerland).

Discussion

The association between MUSKs and healthy life expectancy is substantial and can be characterised as follows:
a) Biological plausibility. The multiple tools of the Swiss army knife are likely to provide some survival capability to their owners by promoting an outdoor lifestyle and physical activity, offering various protective possibilities (e.g., self-defense, shelter building), facilitating a healthy diet (e.g., regular moderate wine consumption, omega-3 fatty acid intake), being available for emergency surgery (e.g., abscess incision, tracheotomy), among others.
b) Strength. The relation between MUSKs and healthy life expectancy is significant (Pearson’s correlation, r = 0.43, p <0.05) and a linear regression performed on low and high income countries showed a significant positive relation.
c) Consistency and dose-response. The analysis included data from 40 countries and the association remained significant after stratification by income groups; the linearity of the relation suggests a dose-effect relationship.
d) Analogy. Other Swiss quality products can have a positive impact on life expectancy: a correlation between chocolate intake per capita and the number of Nobel laureateshas been shown, as well as the longer life expectancy of the Nobel prizewinners compared with the male population of USA [1].
These features and others are detailed in the main text are available online, as is the discussion about limitations, implications and future research.

Conclusion

This ecological study suggests that the use of Swiss army knives is associated with increased life expectancy in both high and low income countries. Governments should adopt strategies to increase the rate of purchase of Swiss army knives and could thus contribute to decrease health disparities between countries.
Note
This is a short version of the original article available online at www.primary-hospital-care.ch, attached to this article.

Qu’avons-nous appris avec cette étude?

Toute corrélation n’est pas bonne à prendre! Un sens critique est toujours nécessaire. Sur le plan épidémiologique, il faut toujours se poser la question si d’autres facteurs non mesurés peuvent expliquer une association apparente. Dans le cas qui nous occupe, il est évident, et vous l’aurez tous deviné, que l’espérance de vie d’un pays est directement liée au statut ­socio-économique de sa population, qui est lui-même associé à la possibilité d’acheter des outils chers comme le couteau suisse, et non l’association directe entre l’espérance de vie et la possession d’un couteau suisse!
Morale de cette histoire: restez vigilants lorsqu’une étude présente des ­corrélations surprenantes … Ce qui ne vous empêchera pas de prendre un couteau suisse quand vous partirez en picnic, cela peut toujours servir, à défaut d’augmenter votre espérance de vie!
Nicolas Senn
Dr Nicolas Senn
Consultation de médecine générale Policlinique
médicale universitaire
Rue de Bugnon 44
CH-1004 Lausanne
nicolas.senn[at]hospvd.ch
1 Messerli FH. Chocolate consumption, cognitive function, and Nobel laureates. N Engl J Med. 2012;367(16):1562–4.

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