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Table 3 Study-level characteristics distribution, overall and comparison across risk factors

From: Epidemiologic studies of modifiable factors associated with cognition and dementia: systematic review and meta-analysis

  Overall EDU SMOK ALCO PA CAFF ANTIOX HCY N-FA P*
N = 247 N = 52 N = 36 N = 30 N = 28 N = 18 N = 27 N = 33 N = 23
Year, Mean (SD) 2004.5 (5.1) 2001.3 (6.3) 2003.6 (5.2) 2004.5 (4.5) 2006.7 (3.6) 2007.7 (4.5) 2003.8 (3.8) 2006.2 (3.1) 2006.9 (4.0) <0.001
Country, N (%)                    
US 98 (39.7) 16 (30.8) 12 (33.3) 15 (50.0) 17 (63.0) 3 (16.7) 17 (63.0) 13 (39.4) 5 (21.7) 0.020
Europe 104 (42.1) 22 (42.3) 18 (50.0) 9 (30.0) 8 (28.6) 10 (55.6) 8 (29.6) 14 (42.4) 15 (65.2)  
Other 45 (18.2) 14 (26.9) 6 (16.7) 6 (20.0) 3 (10.7) 5 (27.8) 2 (7.4) 6 (18.2) 3 (13.00  
Age group, N (%)                    
Excludes < 65y 147 (59.5) 31 (59.6) 17 (47.2) 13 (43.3) 24 (85.7) 12 (66.7) 20 (74.1) 16 (48.5) 14 (60.9) 0.012
Includes < 65y 100 (40.5) 21 (40.4) 19 (52.8) 17 (56.7) 4 (14.3) 6 (33.3) 7 (25.9) 17 (51.5) 9 (39.1)  
Sex, N (%)                    
Both 208 (84.2) 47 (90.4) 28 (77.8) 28 (93.4) 19 (67.9) 16 (88.9) 22 (81.5) 28 (84.8) 20 (87.0) 0.12
Men only 26 (10.5) 3 (5.8) 8 (22.2) 1 (3.3) 5 (17.9) 2 (11.1) 2 (7.4) 3 (9.1) 2 (8.7)  
Women only 13 (5.3) 2 (3.8) 0 (0.0) 1 (3.3) 4 (14.3) 0 (0.0) 3 (11.1) 2 (6.1) 1 (4.3)  
Study design, N (%)                    
Cross-sectional 80 (32.4) 25 (48.1) 7 (19.4) 12 (40.0) 4 (14.3) 7 (38.9) 6 (22.2) 14 (42.4) 5 (21.7) 0.012
Cohort 167 (67.6) 27 (51.9) 29 (80.6) 18 (60.0) 24 (85.7) 11 (61.1) 21 (77.8) 19 (57.6) 18 (78.3)  
Sample size, Mean (SD) 3,561 (5,128) 4,345 (6,066) 4,745 (6,859) 4,745 (6,808) 3,322 (3,927) 2,408 (2,385) 3,643 (4,191) 1,074 (769) 3,061 (3,389) 0.05
Cognitive outcome count, N (%)                    
1 179 (72.5) 34 (65.4) 26 (86.7) 26 (86.7) 20 (71.4) 14 (77.8) 22 (81.5) 21 (63.6) 15 (65.2) 0.77
2 60 (24.3) 15 (28.8) 4 (13.3) 4 (13.3) 7 (25.0) 3 (16.7) 4 (14.8) 10 (30.3) 8 (34.8)  
3 5 (2.0) 2 (3.9) 0 (0.0) 0 (0.0) 1 (3.6) 1 (5.6) 0 (0.0) 1 (3.0) 0 (0.0)  
4 2 (1.2) 1 (1.9) 0 (0.0) 0 (0.0) 0 (0.0) 0 (0.0) 1 (3.7) 1 (3.0) 0 (0.0)  
Cognitive outcome type, N (%)                    0.042
AD/dementia/impairment 114 (46.2) 26 (50.0) 20 (55.6) 6 (20.0) 16 (57.1) 5 (27.8) 15 (55.6) 15 (45.5) 11 (47.8)  
Cognitive function/decline 126 (51.0) 25 (48.1) 16 (44.4) 24 (80.0) 10 (35.7) 11 (61.1) 12 (44.4) 17 (51.5) 11 (47.8)  
Both 7 (2.8) 1 (1.9) 0 (0.0) 0 (0.0) 2 (7.1) 2 (11.1) 0 (0.0) 1 (3.0) 1 (4.4)  
Study finding, N(%)                    0.004
Against hypothesis 5 (2.0) 1 (1.9) 1 (2.8) 2 (6.7) 1 (3.6) 0 (0.0) 0 (0.0) 0 (0.0) 0 (0.0)  
Null 45 (18.2) 4 (7.7) 11 (30.6) 4 (13.3) 0 (0.0) 5 (27.8) 9 (33.3) 6 (18.2) 6 (26.1)  
Positive 152 (61.5) 39 (75.0) 18 (50.0) 17 (56.7) 25 (89.3) 7 (38.9) 11 (40.7) 23 (69.7) 12 (52.2)  
Partially positive (outcomes/exposures) 21 (8.5) 6 (11.5) 2 (5.6) 2 (6.7) 0 (0.0) 3 (16.7) 2 (7.4) 1 (3.0) 1 (4.3)  
Partially positive (sub-groups) 24 (9.7) 2 (7.7) 4 (11.1) 5 (16.7) 2 (7.1) 3 (16.7) 5 (27.8) 3 (9.1) 4 (17.4)  
  1. *P-value for difference across risk/protective factors was obtained from one-way ANOVA test when variable is continuous and χ 2 test when variable is categorical.