Table 1.

Selected characteristics of study participants and withdrawals; individuals aged 75 years in 2003, Niigata City, Japan

	Participants (n 264)		Withdrawals† (n 70)
Variable	Mean or n	sd or %	Mean or n	sd or %	P‡
Dental conditions
Number of teeth at baseline	18·4	8·4	16·6	8·5	0·129
Number of teeth at follow-up	17·8	8·4	N/A				N/A
Number of lost teeth	0·6	1·1	N/A				N/A
Average CAL at baseline	3·3	1·0	3·4	1·0	0·410
Average CAL at follow-up	3·4	1·1	N/A				N/A
Number of teeth with periodontal disease progression	1·5	2·2	N/A				N/A
Demographic and socio-economic status
Gender
Men	141	53·4	32	45·7	0·252
Women	123	46·6	38	54·3
Lower income	30	11·4	13	18·6	0·109
Lower education	148	56·1	39	55·7	0·959
Health status and health behaviours
BMI (kg/m2)	23·0	3·0	22·5	3·1	0·192
Hypoalbuminaemia	103	39·0	23	32·9	0·345
Hyperglyacemia	22	8·3	5	7·1	0·745
Smoking status
Smoker	126	47·7	32	45·7	0·764
Non-smoker	138	52·3	38	54·3
Brushing frequency
<2/d	82	31·1	17	24·3	0·270
≥2/d	182	68·9	53	75·7
Devices for inter-dental cleaning
Not used	130	49·2	39	55·7	0·336
Used	134	50·8	31	44·3
Regular dental visits
No	123	46·6	37	52·9	0·351
Yes	141	53·4	33	47·1

CAL, clinical attachment level; N/A, not available.

Lower income = annual household income <2 000 000 Japanese Yen; lower education = school attendance ≤10 years; hypoalbuminaemia = albumin ≤4·0 g/dl; hyperglycaemia = HbA1c ≥6·5 %; regular dental visits = having regular periodontal examination and professional teeth cleaning at least once annually.

†Withdrawal = person who participated in baseline examination but did not return for follow-up (n 69) and person who became edentulous during the study (n 1).

‡P value for the comparison of selected characteristics between participants and withdrawals.