The model additionally including an indicator for cold wave showed that the days within the cold wave period had an estimated average 4.0%9595% CI = 1.9%, 6.1%, p =.0001) mortality after adjustment for all other variables.
A study using data from 1987 2000 for 99 U.S. cities examined the additional effect of cold waves after adjustment for the cold temperature mortality response [ 19].
The additional effect of cold waves was higher for males, 4.6%, than for females, 1.9%, and was negligible for the 45 64 and 85+ age groups, but was 2.8% and 9.9% for the 65 74 and 75 84 age groups, respectively.
While an association between cold temperatures and higher mortality is well established, relatively few studies have examined the independent effect of cold waves, after controlling for the effect of individual cold days.
Persons living in medium to high wealth municipalities experienced significant increases in mortality with successive colder temperatures among the populations above and below age 65, and with duration of cold waves in high wealth municipalities for ages 65 and above.
The specific effect of cold waves was modeled using a separate indicator variable for the period of the cold wave.
The U.S. study did consider the possible lagged effects of cold waves, up to 7 days [ 19], but used a looser definition of cold waves, 2 consecutive days with cold temperature, vs. 5 for our study.
One possible explanation for the difference between our finding and those from the Taiwanese and U.S. studies is differences in the definition of cold waves.
Duration of cold waves appeared to affect the very elderly population the most.
This study found no additional cold wave effect and in fact found a small but statistically significant decrease in deaths for the 'coldest' cold waves, those with temperatures below the 1st percentile [ 19].
