Thursday, 12 May 2011

A statistical analysis of empircal measures of the weight of the human soul

What is the weight of the human soul?

In 1907, Dr Duncan MacDougall, M.D.of Haverhill, Mass., set out to precisely measure the weight of the human soul. He conducted an experiment involving six hapless souls that were terminal and carefully measured their changes in mass (due to respiration, sweating, etc) while lying on a bed hooked up to a scale, and then the change in mass upon moment of expiration...

He noted:  "[When subject No. 1] expired...suddenly coincident with death the beam end dropped with an audible stoke [CLANG!] hitting against the lower limiting bar and remaining there with no rebound"  - the loss was ascertained to be three-fourths of an ounce.

All other five patients demonstrated similar losses in mass upon death (one took a while - the scale hovered up and down..).

His results were published in American Medicine, April, 1907. See paper at:

Here I present a careful statistical analysis of his data (originally in ounces but converted to grams) to assess the plausibility of his results.


A two-tailed paired T-test of mass change upon death (pairs were the six human subjects) was conducted to test the null hypothesis of zero mean (average) change in mass upon death  - i.e. no measurable soul.

Test statistic t = 4.60 on 5 d.f. Probability = 0.006

Mean loss in mass =  29.23 g (standard error: 6.352).

After accounting for losses in body mass before and immediately after death, it appears there is a consistent, statistically significant loss of body mass of between 0.2-0.6% of the fresh (live) mass. On average, this loss - the assumed mass of the human soul - was just less than 30 g, or less than one third the mass of a standard Cadbury chocolate bar.

1. Dr MacDougall repeated the same experiment on a number of dogs (he didn't wait patiently until they expired) and found the average change in mass to be zero, suggesting the absence of a measurable soul.

2. The film 21 Grams, starring Sean Penn, was named after subject number 1 (see above table) whose soul weighed 21 g. But please note that the average human soul appears to be about 8 g heavier than this.



1 comment:

  1. So, based your research, i further hypothesise that the more chocolate one eats the heavier their soul will weigh at the point of death. Eureka, I do believe I have found the subject matter for my PhD at long last!