Table 4.

Increases in neonatal mortality connected with being born in time periods which put infants at risk during the 1918–19 influenza epidemic in Derbyshire: different causes of death examined separately

	Odds ratios associated with periods of birtha
	July 1918–Jan. 1919	Jan.–April 1919
All causes	1.326**	1.776***
Prematurity, wasting, congenital malformation	1.256	1.762***
Bronchitis and pneumonia	1.624	2.444*
Complications of labour	1.110	0.000
Convulsions	1.103	0.799
Other causes (including influenza)	1.637*	2.417***

^aOdds ratios give the multiplicative increase in mortality associated with period of birth, compared to a value of 1.000 for all other months in the period 1917–1922. Each odds ratio is derived from a separate multivariate hazards analysis, in which other variables are also controlled (see text for details).

^***Significant at 1% level.

^**Significant at 5% level.

^*Significant at 10% level.

Source: Derbyshire health visitor data.