How fast does the Grim Reaper walk? Receiver operating characteristics curve analysis in healthy men aged 70 and overBMJ 2011; 343 doi: https://doi.org/10.1136/bmj.d7679 (Published 15 December 2011) Cite this as: BMJ 2011;343:d7679
- Fiona F Stanaway, research fellow1,
- Danijela Gnjidic, research fellow234,
- Fiona M Blyth, deputy director, Concord Health and Ageing in Men Project245,
- David G Le Couteur, professor of geriatric medicine246,
- Vasi Naganathan, staff specialist, associate professor24,
- Louise Waite, staff specialist24,
- Markus J Seibel, professor of endocrinology6,
- David J Handelsman, director, professor26,
- Philip N Sambrook, professor27,
- Robert G Cumming, professor of geriatric medicine and epidemiology124
- 1Sydney School of Public Health, University of Sydney, Sydney, Australia
- 2Sydney Medical School, University of Sydney, Sydney, Australia
- 3Department of Clinical Pharmacology and Department of Aged Care, Royal North Shore Hospital, Sydney, Australia
- 4Centre for Education and Research on Ageing, Concord Hospital, Sydney, Australia
- 5Sax Institute, Sydney, Australia
- 6ANZAC Research Institute, Concord Hospital, Sydney, Australia
- 7Kolling Institute of Medical Research, Institute of Bone and Joint Research, Royal North Shore Hospital, Sydney, Australia
- Correspondence to: D Gnjidic
- Accepted 21 November 2011
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.
Contributors: FFS conceived, designed, and funded the study, analysed and interpreted the data, and drafted and critically revised the article. FFS, DG, FMB, DGLeC, VN, LW, MJS, DJH, PNS and RGC helped design the study, analyse and interpret the data, and critically revise the article. FFS is guarantor. All authors had full access to the data and take responsibility for its integrity and the accuracy of the analysis.
Funding: The CHAMP study is funded by the Australian National Health and Medical Research Council (grant No 301916), Sydney Medical School Foundation, and Ageing and Alzheimer’s Research Foundation. The funding source had no involvement in the study design, analysis, interpretation, or decision to submit this work.
Competing interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declare: no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; and no other relationships or activities that could appear to have influenced the submitted work.
Ethical approval: This study was approved by the Sydney South West Area Health Service human research ethics committee. All participants gave informed consent.
Data sharing: No additional data available.
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