Table 1.

Descriptive statistics on Puget Sound area (ACT) cohort based on baseline information (1994–2018) for individuals with nonmissing APOE; total and stratified by above/below mean-centered baseline $\mathrm{P}{\mathrm{M}}_{2.5}$.^a Continuous variables reported as mean (± SD); categorical variables reported as n (%)^b.

	Total ($\mathit{n}=\mathrm{4,166}$)	Mean-centered baseline 10-y average ${\mathrm{PM}}_{2.5}$
		$\le \text{Mean}$	$>\text{Mean}$
		($\mathit{n}=\mathrm{1,413}$)	($\mathit{n}=\mathrm{2,753}$)
Intake age (y)	75 ($\pm 6.3$)	73 ($\pm 6.0$)	76 ($\pm 6.2$)
Sex
Male	1,748 (42 %)	627 (44 %)	1,121 (41 %)
Female	2,418 (58 %)	786 (56 %)	1,632 (59 %)
ACT cohort
Original (1994–1996)	2,135 (51 %)	1 (0 %)	2,134 (78 %)
Expansion (2000–2003)	651 (16 %)	48 (3 %)	603 (22 %)
Replacement (2005–2018)	1,380 (33 %)	1,364 (97 %)	16 (1 %)
Birth cohort
$1890–<1910$	162 (4 %)	0 (0 %)	162 (6 %)
$1910–<1915$	325 (8 %)	6 (0 %)	319 (12 %)
$1915–<1920$	627 (15 %)	30 (2 %)	597 (22 %)
$1920–<1925$	890 (21 %)	79 (6 %)	811 (29 %)
$1925–<1930$	790 (19 %)	126 (9 %)	664 (24 %)
$1930–<1935$	425 (10 %)	245 (17 %)	180 (7 %)
$\ge 1935$	947 (23 %)	927 (66 %)	20 (1 %)
$\ge 1$ APOE $\mathbf{\epsilon }4$ allele
Yes	1,103 (26 %)	403 (29 %)	700 (25 %)
No	3,063 (74 %)	1,010 (71 %)	2,053 (75 %)
Race
White	3,760 (90 %)	1,259 (89 %)	2,501 (91 %)
Non-White	406 (10 %)	154 (11 %)	252 (9 %)
Year 2000 census tract median household income ($USD)
$<\mathrm{35,000}$	383 (9 %)	111 (8 %)	272 (10 %)
$\mathrm{35,000}–<\mathrm{50,000}$	1,292 (31 %)	387 (27 %)	905 (33 %)
$\mathrm{50,000}–<\mathrm{75,000}$	2,048 (49 %)	730 (52 %)	1,318 (48 %)
$\ge \mathrm{75,000}$	443 (11 %)	185 (13 %)	258 (9 %)
Degree
None	345 (8 %)	26 (2 %)	319 (12 %)
GED/HS	1,623 (39 %)	314 (22 %)	1,309 (48 %)
Bachelor’s	966 (23 %)	387 (27 %)	579 (21 %)
Master’s	614 (15 %)	367 (26 %)	247 (9 %)
Doctorate	244 (6 %)	129 (9 %)	115 (4 %)
Other	374 (9 %)	190 (13 %)	184 (7 %)
Smoking status
Never	2,019 (48 %)	712 (50 %)	1,307 (47 %)
Past	1,947 (47 %)	667 (47 %)	1,280 (46 %)
Current	200 (5 %)	34 (2 %)	166 (6 %)
Regular exercisec
Yes	3,021 (73 %)	1,040 (74 %)	1,981 (72 %)
No	1,145 (27 %)	373 (26 %)	772 (28 %)
BMI
Underweight	35 (1 %)	8 (1 %)	27 (1 %)
Normal	1,304 (31 %)	427 (30 %)	877 (32 %)
Overweight	1,764 (42 %)	601 (43 %)	1,163 (42 %)
Obese	1,063 (26 %)	377 (27 %)	686 (25 %)
Diabetes
Yes	436 (10 %)	167 (12 %)	269 (10 %)
No	3,730 (90 %)	1,246 (88 %)	2,484 (90 %)
Heart disease
Yes	690 (17 %)	147 (10 %)	543 (20 %)
No	3,476 (83 %)	1,266 (90 %)	2,210 (80 %)
CVD
Yes	360 (9 %)	89 (6 %)	271 (10 %)
No	3,806 (91 %)	1,324 (94 %)	2,482 (90 %)
Hypertension
Yes	1,680 (40 %)	622 (44 %)	1,058 (38 %)
No	2,486 (60 %)	791 (56 %)	1,695 (62 %)
CASI IRT (Crane et al. 2008) score	0.35 ($\pm 0.70$)	0.54 ($\pm 0.64$)	0.26 ($\pm 0.70$)
Moved during ACT follow-up
Yes	2,350 (56 %)	422 (30 %)	1,928 (70 %)
No	1,806 (43 %)	988 (70 %)	818 (30 %)
Missing	10 (0.2%)	3 (0.2%)	7 (0.3%)
Dementia diagnosisd
Yes	1,138 (27 %)	175 (12 %)	963 (35 %)
No	3,028 (73 %)	1,238 (88 %)	1,790 (65 %)
Alzheimer’s disease diagnosisd
Yes	921 (22 %)	144 (10 %)	777 (28 %)
No	3,245 (78 %)	1,269 (90 %)	1,976 (72 %)

Note: ACT, Adult Changes in Thought; AD, Alzheimer’s disease; APOE, apolipoprotein E; BMI, body mass index; CASI IRT, Cognitive Assessment Screening Instrument Item Response Theory; CVD, cardiovascular disease; GED, general equivalency diploma; HS, high school; USD, U.S. dollars.

^aStratification by year-specific mean-centered exposure averages removes the influence of the strong temporal variation and focuses on within-year population comparisons. To calculate the mean-centered values, we subtracted the year-specific [(i.e., time-varying, based on baseline (entry) year] mean across 10-y average ${\mathrm{PM}}_{2.5}$ exposures from each 10-y average ${\mathrm{PM}}_{2.5}$ exposure.

^bMissingness reported for “Never moved during ACT follow-up.” Other variables had missingness of less than $<2\%$ in the original data set. As described in the text, we imputed missing values of non-APOE covariates (median household income, degree, smoking status, BMI category, diabetes, heart disease, CVD, hypertension) with the mean category or value of each to prevent individuals from dropping out of the subsequent inverse probability weighting selection model process.

^cRegular exercise refers to self-reported exercise for at least 15 minutes three times per week.

^dDementia and AD-subtype dementia case numbers reflect diagnoses across the entire study population. Case numbers may vary in specific analyses based on inclusion criteria; e.g., the primary analysis based on 10-y average exposure has two fewer dementia cases due to missing 10-y average exposure data.