Ambient temperature variation does not influence regional proportion of human male births in New Zealand

Figures & data

Figure 1  Map showing the location of different regions in New Zealand used for the analysis. Note that these regional boundaries are those defined by Statistics New Zealand in 1961. n _t =total number of births in dataset; n _y =average number of births per year.

Figure 2  The relationship across regions between the mean annual ambient temperature and average proportion of male births (both averaged over 1961–2009). Error bars are 95% confidence intervals.

Figure 3  Time series of the proportion of male births and average annual ambient temperature in two contrasting New Zealand regions. A, The warmest region, Northland (overall mean ambient temperature of 15.15 °C). B, The coldest region, Southland (overall mean ambient temperature of 9.87 °C).

Table 1  Model coefficients from time series analysis using transfer function (ARIMA) models to estimate the dynamic effects of mean annual ambient temperature on the proportion of males born. This analysis tested for a positive relationship between current or lagged mean annual ambient temperature and the proportion of male births. Only two of 13 coefficients were statistically significant (P < 0.05) for the current year temperature, and just one for the first lag of temperature, with those three coefficients all negative n=49 years of data.

Region	Current year temperature			First lag of temperature
	ß	SE(ß)	P	ß	SE(ß)	P
Northland	0.001	0.003	0.856	0.005	0.003	0.113
Central Auckland	0.002	0.001	0.077	0.002	0.001	0.125
South Auckland/ Bay of Plenty	−0.003	0.002	0.053	−1.4×10^−4	0.002	0.927
East Coast	1.1×10^−4	0.004	0.978	−0.004	0.004	0.338
Hawke's Bay	0.002	0.003	0.591	0.004	0.003	0.125
Taranaki	−0.004	0.003	0.194	−0.003	0.003	0.33
Wellington	−0.002	0.002	0.179	0.002	0.002	0.394
Marlborough	0.005	0.008	0.531	−0.008	0.008	0.284
Nelson	−0.011	0.004	0.008	−0.009	0.004	0.046
Westland	−0.008	0.005	0.102	−0.003	0.005	0.533
Canterbury	−0.003	0.002	0.145	0.001	0.002	0.689
Otago	0.003	0.003	0.297	−0.001	0.003	0.633
Southland	−0.014	0.004	0.002	−0.003	0.004	0.432