Table 1. Atrial Fibrillation Incidence Rates and Age-adjusted Period Prevalence by Sex and Decade.

	Decade of Atrial Fibrillation
	1958-1967	1968-1977	1978-1987	1988-1997	1998-2007	P for Trend*
Men
No. at risk	1925	2399	2569	2595	2128
Person-years at risk	14044	17448	19223	19196	17270
Mean age, years†	55·0±5•8	58•6±8•1	60•4±9•9	60•8±10•6	63•1±10•5
Atrial fibrillation cases, no.	40	101	166	266	248
Crude incidence rate	2•85	5•79	8•64	13•86	14•36	<0•0001
Age-adjusted incidence rate§	3•70	7•31	9•07	14•32	13•37	<0•0001
Age-adjusted period prevalence	20•4	37•7	52•3	81•8	96•2	<0•0001
Atrial fibrillation based on Framingham Heart Study clinic ECGs
Atrial fibrillation cases, no.	23	38	56	70	81
Crude incidence rate	1•61	2•12	2•81	3•43	4•30	<0•0001
Age-adjusted incidence rate§	1•83	2•55	2•86	3•35	3•75	0•06
Age-adjusted period prevalence	12•6	19•1	24•0	25•7	25•7	0•0007
Women
No. at risk	2401	2924	3174	3315	2857
Person-years at risk	18356	23360	25254	25046	23220
Mean age, years†	55•0±5•8	59•6±8•4	62•7±10•7	62•9±11•8	64•7±11•9
Atrial fibrillation cases, no.	35	90	161	194	243
Crude incidence rate	1•91	3•85	6•38	7•75	10•47	<0•0001
Age-adjusted incidence rate§	2•52	4•69	5•47	6•14	8•55	<0•0001
Age-adjusted period prevalence	13•7	25•1	29•5	34•3	49•4	<0.0001
Atrial fibrillation based on Framingham Heart Study clinic ECGs
Atrial fibrillation cases, no.	21	46	51	50	52
Crude incidence rate	1•10	1•88	1•93	1•91	2•13	0•03
Age-adjusted incidence rate§	1•31	2•11	1•64	1•40	1•58	0•13
Age-adjusted period prevalence	8•1	14•8	13•9	12•6	11•8	0•009

Age 50-89 years, free of atrial fibrillation.

^*P for trend was obtained using Poisson Regression.

^†Mean age is for the population at risk for development of atrial fibrillation. Age is the earliest eligible age within a decade.

Atrial fibrillation incidence rates are per 1000 person-years of follow up.

Atrial fibrillation prevalence rates are person-years lived by atrial fibrillation individuals per 1000 total person-years lived during each period, i.e. by all person-years contributed by survivors at the beginning of the period. Atrial fibrillation cases include all those participants who developed atrial fibrillation in or before the corresponding period.

^§Adjusted incidence rates were calculated using direct standardization of sex-pooled and time-pooled 10-year age groups. For the first period, given that there was no subject in the 80-90 age group, the incidence rates were standardized to the overall distribution among the remaining age groups only.