Table 2. Characteristics of the study population in 1998 (N = 6808).

		n	%
Demographic factors
Age	1 year	3983	59
	2 years	950	14
	3 years	871	13
	4 years	886	13
Sex	Male	3547	52
	Female	3261	48
Ethnicity	White	4986	73
	South Asian	1822	27
Perinatal and early life factors
Low birth weight (<2500g)		473	7
Gestational age <37 weeks		418	6
Breastfed		4035	60
Environmental exposures
Nursery care		2985	44
Mother smoking (postnatally)		1349	20
Other person smoking in household		1744	26
Socioeconomic factors
Higher parental education#		2851	42
More deprived (Townsend deprivation index)¶		1332	20
Parental history of atopic diseases
Hay fever (mother or father)		2954	43
Wheeze or asthma (mother or father)		1955	29
Symptoms
Wheeze		2025	30
Asthma (doctor diagnosed) +		550	17
Gastroesophageal reflux (frequent posseting)		1044	15
Frequent colds§		1194	18
Coughing more than peers+		328	10
Cough with colds		4849	71
Cough without colds		2150	32
Night cough		1809	27
Cough triggered by:
Exercise/play		877	14
Laughter/crying+		756	22
House dust+		105	3
Pollenf		-	-
Pets		118	2
Food/drinks		700	11

^#: age at the end of education is >16 years;

^¶: Townsend Deprivation Index: more affluent [-6.222, -2.635], affluent [-2.615, -0.707], average [-0.705, 1.859], deprived [1.861, 5.147], more deprived [5.160, 11.072];

⁺: the question was asked only in a subcohort;

^§: ≥7 colds in the last 12 months;

^f: not asked in the 1998 survey.