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Table 1 Baseline characteristics of study participants.

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. (%)

     

   Female

10 (12)

17 (20)

27 (16)

   Male

73 (88)

68 (80)

141 (84)

Completed education - no. (%)

     

   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. (%)

     

   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. (%)

     

   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. (%)

     

   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)

 
  1. *Received 300 mg caffeine twice, described as caffeine (overt) or as placebo (covert) in a balanced randomized cross-over design. †Received placebo twice, described as placebo (overt) or as caffeine (covert) in a balanced randomized cross-over design. ‡ Measured on 100 mm visual analogue scale.