The Hound of the Baskervilles effect: natural experiment on the influence of psychological stress on timing of death

Abstract

Objective: To determine whether cardiac mortality is abnormally high on days considered unlucky: Chinese and Japanese people consider the number 4 unlucky, white Americans do not.

Design: Examination of cardiac and non-cardiac mortality on and around the fourth of each month in Chinese and Japanese subjects and white controls.

Setting: United States.

Subjects: All Chinese and Japanese (n=209 908) and white (n=47 328 762) Americans whose computerised death certificates were recorded between the beginning of January 1973 and the end of December 1998.

Main outcome measures: Ratio of observed to expected numbers of deaths on the fourth day of the month (expected number was estimated from mortality on other days of the month).

Results: Cardiac mortality in Chinese and Japanese people peaked on the fourth of the month. The peak was particularly large for deaths from chronic heart disease (ratio of observed to expected deaths = 1.13, 95% confidence interval 1.06 to 1.21) and still larger for deaths from chronic heart disease in California (1.27, 1.15 to 1.39). Within this group, inpatients showed a particularly large peak on the fourth day(1.45, 1.19 to 1.81). The peak was not followed by a compensatory drop in number of deaths. White controls, matched on age, sex, marital status, hospital status, location, and cause of death, showed no similar peak in cardiac mortality.

Conclusions: Our findings of excess cardiac mortality on “unlucky” days are consistent with the hypothesis that cardiac mortality increases on psychologically stressful occasions. The results are inconsistent with nine other possible explanations for the findings—for example, the fourth day peak does not seem to occur because of changes in the patient's diet, alcohol intake, exercise, or drug regimens.