Body mass index, occupational activity, and leisure-time physical activity: an exploration of risk factors and modifiers for knee osteoarthritis in the 1946 British birth cohort

Table 1 Description of the cohort, stratified by gender

	Total		Men		Women
	Mean (SD)	N	Mean (SD)	N	Mean (SD)	N	p-value^a
Body mass index (kg/m²) at 36y	24.1 (3.7)	2646	24.8 (3.2)	1289	23.5 (3.9)	1357	<0.001
Body mass index (kg/m²) at 43y	25.4 (4.2)	2745	25.7 (3.5)	1336	25.2 (4.7)	1409	0.001
Body mass index (kg/m²) at 53y	27.4 (4.8)	2917	27.4 (4.0)	1438	27.4 (5.5)	1479	0.812
	%	N	%	N	%	N	p-value ^a
Knee osteoarthritis clinical observation at 53y
Yes	10.2	302	7.5	109	12.8	193	<0.001
Disabling/life-threatening health conditions at 53y	11.9	353	11.6	169	12.2	184	0.604
1 or more
Family history of arthritis
Yes	39.3	1099	35.5	486	42.9	613	<0.001
History of knee injury
Yes	22.8	673	27.5	399	18.2	274	<0.001
Education at 26y
Degree or higher	9.9	277	14.8	203	5.2	74
GCE ‘A’ level, Burnham B or A2	25.6	714	28.0	384	23.3	330
GCE ‘O’ level or Burnham C	20.1	561	14.6	200	25.5	361
Sub GCE or vocational course	7.5	208	5.9	82	8.9	126
No qualifications	36.9	1031	36.7	504	37.2	527	<0.001
Income at 53 y
>£50,000	8.4	234	9.7	137	7.0	97
£25,000-£49,999	26.1	732	27.7	391	24.5	341
<£24,999	65.5	1835	62.6	882	68.5	953	0.002

ISSN: 1471-2474