Table 2.

Polysomnographic Measures for the Control Group and MJ Users on Sleep Nights 1 and 2

Variable	Night 1 Control Group (n = 14)	Night 2 MJ Group (n = 17)	t/U (P level)	d#	Control Group (n = 14)	MJ Group (n = 17)	t/U (P level)	d#
Total sleep time (TST)(min)	459 (42)	420 (62)	0.05*	0.75	461 (33)	413 (79)	0.04*A	0.75
Sleep efficiency (TST/TIB)	0.94 (0.05)	0.91 (0.08)	0.17	0.42	0.94 (0.04)	0.89 (0.06)	0.01**	1.04
U Initial sleep latency (ISL)(min)	7 (11)	16 (28)	0.40	0.41	5 (5)	22 (27)	0.003**	0.77
Initial REM latency (min)	109 (49)	77 (70)	0.16	0.52	116 (65)	77 (45)	0.04*	0.71
Slow wave sleep (SWS)/Stage 3/4 (min)	74 (32)	29 (22)	0.001**	1.67	70 (27)	27 (26)	0.001**	1.63
Slow wave sleep (SWS)/Stage 3/4 (%TST)B	16 (7)	7 (6)	0.001**	1.41	15 (6)	7 (7)	0.001**	1.26
Stage REM (min)	99 (27)	94 (40)	0.70	0.14	97 (23)	87 (30)	0.30	0.61
Stage REM (% TST)	21 (5)	23 (9)	0.59	0.32	21 (5)	21 (5)	0.21	0
UPLM index (median #/hr)	1.5	2.6	0.07		2.4	3.4	0.52
XFrequency of group with PLM (% with PLM)	2/14 (14%)	9/17 (53%)	0.12		4/14 (29%)	7/17 (41%)	0.71
UWake after sleep onset (min)	20 (19)	24 (21)	0.36	0.19	22 (18)	23 (18)	0.63	0.05

Note. Numbers are means (standard deviations) TST = total sleep time: TIB (min): time in bed (min): PLM = periodic leg movements without and with (PLMA) arousals; ^U Mann-Whitney used for analyses. ^XChi-square used for frequency data. ^AGroup differences became nonsignificant after controlling for Shipley IQ score on Night 2. ^BGroup differences remained significant after controlling for education on Night 1 and Night 2. d^# = Cohen's d was used to estimate effect size. Reference Values from the JHB sleep clinic for 20–39 year olds: total sleep time 455 (33), initial sleep latency 16 (14), wake after sleep onset 12 (8), SWS (min) >58 min = within normal limits