死神の歩行速度は？

2011年12月発行のBMJ = British Medical Journal = によると、オーストラリアのシドニーの研究チームが70歳以上の男性1,705人を対象に、5年間にわたって歩行速度と死亡率の関係を調査した。

●被験者1,705人の平均歩行速度は秒速0.88mだった。

●5年間の追跡調査中、被験者1,705人中266人が死亡した。

●秒速0.82mを境界にして、速く歩くグループと、遅く歩くグループに分類すると、速く歩くグループの死亡率は1.23倍も低かった。

●秒速1.36m以上の速度で歩く人に死亡者は一人もいなかった。

●つまり、死神の歩行速度は秒速1.36km以下で、『日頃から秒速1.36m以上の歩行速度を心がけていれば、死神に追いつかれることはない』と、この研究は結論づけている。

●秒速1.36m以上とは、分速81.6m（時速4.9m）に相当する。これは、1kmを12.2分で歩く速度である。

---

How fast does the Grim Reaper walk? Receiver operating characteristics curve analysis in healthy men aged 70 and over

BMJ 2011; 343 doi: http://dx.doi.org/10.1136/bmj.d7679 (Published 15 December 2011)

Abstract

Objective To determine the speed at which the Grim Reaper (or Death) walks. Design Population based prospective study. Setting Older community dwelling men living in Sydney, Australia. Participants 1705 men aged 70 or more participating in CHAMP (Concord Health and Ageing in Men Project). Main outcome measures Walking speed (m/s) and mortality. Receiver operating characteristics curve analysis was used to calculate the area under the curve for walking speed and determine the walking speed of the Grim Reaper. The optimal walking speed was estimated using the Youden index (sensitivity+specificity?1), a common summary measure of the receiver operating characteristics curve, and represents the maximum potential effectiveness of a marker. Results The mean walking speed was 0.88 (range 0.15-1.60) m/s. The highest Youden index (0.293) was observed at a walking speed of 0.82 m/s (2 miles (about 3 km) per hour), corresponding to a sensitivity of 63% and a specificity of 70% for mortality. Survival analysis showed that older men who walked faster than 0.82 m/s were 1.23 times less likely to die (95% confidence interval 1.10 to 1.37) than those who walked slower (P=0.0003). A sensitivity of 1.0 was obtained when a walking speed of 1.36 m/s (3 miles (about 5 km) per hour) or greater was used, indicating that no men with walking speeds of 1.36 m/s or greater had contact with Death. Conclusion The Grim Reaper’s preferred walking speed is 0.82 m/s (2 miles (about 3 km) per hour) under working conditions. As none of the men in the study with walking speeds of 1.36 m/s (3 miles (about 5 km) per hour) or greater had contact with Death, this seems to be the Grim Reaper’s most likely maximum speed; for those wishing to avoid their allotted fate, this would be the advised walking speed.