From: Interaction between drug and placebo effects: a cross-over balanced placebo design trial
Characteristics | Caffeine Group* (N = 83) | Placebo Group†(N = 85) | Both Groups (N = 168) | ||
---|---|---|---|---|---|
Age - mean (SD), yr | 30.6 (6.6) | 28.3 (5.7) | 29.4 (6.4) | ||
Sex - no. (%) | Â | Â | Â | Â | Â |
   Female | 10 (12) | 17 (20) | 27 (16) | ||
   Male | 73 (88) | 68 (80) | 141 (84) | ||
Completed education - no. (%) | Â | Â | Â | Â | Â |
   High school | 15 (18) | 7 (8) | 22 (13) | ||
   College | 44 (53) | 54 (64) | 98 (58) | ||
   University | 24 (29) | 24 (28) | 48 (29) | ||
Caffeine consumption - no. (%) | Â | Â | Â | Â | Â |
   100-149 mg/dy | 28 (34) | 23 (27) | 51 (30) | ||
   150-199 mg/dy | 28 (34) | 24 (28) | 52 (31) | ||
   200-249 mg/dy | 15 (18) | 22 (26) | 37 (22) | ||
   250-300 mg/dy | 12 (14) | 16 (19) | 28 (17) | ||
Occupational Status - no. (%) | Â | Â | Â | Â | Â |
   Professional, technical, managerial | 17 (21) | 19 (22) | 36 (22) | ||
   Clerical, sales | 24 (29) | 32 (38) | 56 (34) | ||
   Service | 22 (27) | 25 (29) | 47 (28) | ||
   Agricultural, fishery related | 10 (12) | 1 (1) | 11 (7) | ||
   Students | 6 (7) | 8 (9) | 14 (8) | ||
   Unemployed | 3 (3) | 0 (0) | 3 (2) | ||
Race or ethnic group - no. (%) | Â | Â | Â | Â | Â |
   Saudi | 3 (4) | 9 (11) | 12 (7) | ||
   Arab, non-Saudi | 14 (17) | 11 (13) | 25 (15) | ||
   Asian | 66 (80) | 65 (76) | 131(78) | ||
 | Overt | Covert | Overt | Covert |  |
Caffeine level - mean (SD), μg/ml |  |  |  |  |  |
   Baseline | 0.26 (0.43) | 0.20 (0.34) | 0.30 (0.56) | 0.29 (0.35) |  |
   3-hour | 9.38 (2.86) | 9.08 (2.77) | 0.17 (0.25) | 0.18 (0.24) |  |
Energy level - mean (SD), mm‡ | 71 (25) | 70 (24) | 74 (19) | 74 (20) |  |
Sleepiness level - mean (SD), mm‡ | 19 (22) | 22 (26) | 20 (25) | 20 (20) |  |
Nausea level - mean (SD), mm‡ | 7 (14) | 6 (13) | 8 (18) | 9 (15) |  |
Systolic blood pressure - mean (SD), mm Hg | 121 (14) | 122 (13) | 121 (12) | 122 (12) | Â |