Inclusion of mobile phone numbers into an ongoing population health survey in New South Wales, Australia: design, methods, call outcomes, costs and sample representativeness

Table 4 Sample comparisons to the latest population profile for NSW

Demographic group		Landline frame		Mobile frame		Landline plus mobile only		Both frames combined #		2011 Census
Demographic group		Total (%)	p-value	Total (%)	p-value	%	p-value	%	p-value	2011 Census
Age groups	0-15	14.1	<0.001	11.4	0.03	13.4	<0.001	12.1	0.01	20.5
	16-24	4.1		12.4		5.8		7.3		11.6
	25-34	5.6		23.1		10.2		13.2		13.6
	35-44	7.6		15.0		8.2		9.9		14.1
	45-54	13.0		16.9		12.7		13.4		13.8
	55-64	21.6		12.9		19.8		17.4		11.7
	65-74	18.4		6.5		16.4		14.1		7.8
	75-high	15.6		1.7		13.5		12.5		6.9
Sex	Male	38.9	0.04	48.4	0.85	40.1	0.07	42.8	0.20	49.3
Sex	Female	61.1	0.04	51.6	0.85	59.9	0.07	57.2	0.20	50.7
Aboriginality	Aboriginal	2.2	0.86	2.6	0.94	2.6	0.96	2.6	0.96	2.5
Aboriginality	Non-Aboriginal	97.8	0.86	97.4	0.94	97.4	0.96	97.4	0.96	97.5
Country of birth	Australia	79.4	0.02	64.9	0.42	77.1	0.07	73.4	0.30	68.6
Country of birth	Overseas	20.6	0.02	35.1	0.42	22.9	0.07	26.6	0.30	31.4
Marital status	Married	54.1	<0.001	54.0	0.76	51.3	0.01	51.5	0.08	49.4
	Widowed	13.7		3.1		12.2		11.1		5.8
	Separated	4.0		3.3		3.9		3.7		3.1
	Divorced	12.3		7.1		11.7		10.2		8.3
	Never married	15.9		32.5		20.9		23.5		33.4
Income*	< $20,000	24.0	0.02	12.0	0.04	23.4	0.02	21.9	0.05	13.7
	$20,001-$40,000	19.8		15.4		19.2		18.5		19.8
	$40,001-$60,000	15.1		14.9		15.3		14.7		16.9
	$60,001-$80,000	10.4		14.0		10.8		11.2		19.8
	$80,000 plus	30.8		43.7		31.3		33.7		29.8

Notes: ^# Calculation numbers for combined frame = ((S_a+λS_ab ^A)+ (S_b+(1-λ)S_ab ^B) where S =sample; λ=overlap adjustment (set to 0.5); _A landline sample frame; _B denotes mobile sample frame; _a landline-only phone users; _b mobile-only phone users; _ab denotes both mobile phone and landline users.
* Census income information was converted from weekly income to annual income for the comparison.
χ2 testing, setting the significance level of p<0.05, was used for the comparisons between the sample demographic categories and the population profile (2011 census).