SEASONAL-VARIATION OF MORTALITY-RATES WIT HIN THE CITY OF VALENCIA, SPAIN

Objective. To study the seasonal variation in mortality for all causes , grouped according to age and sex, within the city of Valencia during the period 1976-1990 and its relationship with air temperature. Mater ial and methods. This is an ecological study using monthly global mort ality and mean atmospheric temperature statistics for the city of Vale ncia, Spain between 1976 and 1990. The principal variable has turned o ut to be mortality for all causes. Mortality rates have been determine d for specific age groups (0-4, 35-49, 50-64, 65-74 and greater than o r equal to 75), as well as for both genders, within the city of Valenc ia for each of the 180-month period of investigation. Average monthly mortality data has been obtained and the percentage variation has been calculated. Graphical analysis has been used to examine the seasonal variation in mortality and in order to discern the nature of any relat ionship between atmospheric temperature and mortality. The regression line has been adjusted using the Loess method (smoothed regression mot ive, locally pondered). The association between mean temperature and m ortality has calculated by means of multiple regression analysis contr oling for trend, seasonality and period effect. Results. A clear seaso nal pattern emerges with mortality peaking during the Winter months an d dipping during the Summer and early Autumn. The increase in mortalit y seen during the month of January came to 27.7% of the total mortalit y for females and 19.5% of the total mortality for males. By age group s, this increase was greater in the 75-plus age group. Graphically, th e relationship between temperature and mortality has a V-shape appeara nce, with a lower mortality level when the mean daily temperature for the month in question is approximately 23 degrees Celsius. Based on th is relationship,two complementary variables were constructed and denom inated cold and heat. These variables explain the greater percentage v ariability in mortality for all causes (47.6% in males and 54.8% in fe males) in comparison with the model having temperature as its only var iable. The association between temperature variables and mortality was greater in the older age groups ant in the females. Conclusions. A ma rked seasonal variation in mortality for all causes can be observed fo r both sexes, with peaks in the mortality rate during January and fewe r mortalities during September. The seasonal variation in mortality gr ows in line with age and is undetectable in the youngest age group. By sex, the seasonal pattern is more marked for females than for males, with a noticeably more pronounced positive association between mortali ty and the cold variable in men of the older age-group, whereas, for w omen of the older age group, there is a greater association with the h eat variable.