BACKGROUND AND AIM:Several seasonal variations have been found in birth rates in different countries at different periods. The characteristics of the rhythmic patterns vary according to geographical location and chronological changes. This study presents data on spanish birth seasonality over six decades. METHODS:A time series composed of 33,421,731 births in Spain in the period 1941-2000 was analysed. The series comes from the National Institute of Statistics and was processed according to the following norms: (1) normalisation of the duration of months and years; (2) clinical analysis of temporal series (isolation of seasonal component); (3) Fourier's spectral analysis; and (4) cosinor analysis (adjustment to the cosine curve of two harmonics). RESULTS:Significant seasonal rhythm was found in the set of births, both for a 12-month period and a 6-month period. The rhythm shows bimodal morphology, with a pronounced birth peak in April and a smaller one in September. These peaks correspond to July and December conceptions, respectively. The major birth peak shifted to March-May between the 1940s and the 1980s. Birth rhythm changed after the 1960s, with a decrease in amplitude and later loss of seasonality in the 1990s. CONCLUSIONS:In Spain, seasonal birth rhythm shows a decline from 1970, and, finally, lack of birth seasonality in 1991-2000. This trend is similar to other European countries, although Spain shows a more intense loss of seasonality.

译文

背景与目的:不同国家不同时期的出生率存在多个季节性变化。节奏模式的特征根据地理位置和时间顺序的变化而变化。这项研究提供了过去六十年西班牙出生季节的数据。
方法:分析了一个时间序列,其中包括西班牙在1941-2000年期间的33,421,731例出生。该系列来自美国国家统计局,并根据以下规范进行了处理:(1)数月和数年的历时归一化; (2)时间序列的临床分析(季节成分的隔离); (3)傅立叶光谱分析; (4)余弦分析(调整两个谐波的余弦曲线)。
结果:在一组婴儿中发现了明显的季节性节律,分别为12个月和6个月。这种节律表现出双峰形态,在4月有一个明显的出生高峰,在9月有一个较小的出生高峰。这些高峰分别对应于7月和12月的概念。在1940年代至1980年代之间,主要的出生高峰转移到了3月至5月。 1960年代后出生的节奏发生了变化,在1990年代振幅减小,后来失去了季节性。
结论:在西班牙,季节性出生节律从1970年开始下降,最后在1991-2000年间缺乏出生季节性。尽管西班牙的季节性损失更为严重,但这种趋势与其他欧洲国家类似。

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