Table 2.

Comparisons of psychological construct scores between groups screening positive and negative for insomnia at baseline (entry to university)

	Healthy sleep group,a mean (s.d.)	Insomnia group,b mean (s.d.)	t-Test statisticc	95% CI for difference between meansc	P-valuec
Self-esteem,d cohorts 1 and 2	19.94 (5.27)	15.61 (5.47)	−25.2	−4.67 to −3.99	<0.001
External locus of control,e cohort 1	13.79 (5.11)	16.15 (5.13)	9.76	1.89–2.83	<0.001
Evaluative concerns,f cohort 2	9.98 (2.32)	11.61 (2.28)	16.53	1.44–1.83	<0.001
Personal standards,f cohort 2	16.75 (3.09)	16.90 (3.12)	1.11	−0.11 to 0.41	0.27

^a.Negative screen for insomnia, using the Sleep Condition Indicator with threshold score of 16.

^b.Positive screen for insomnia, using the Sleep Condition Indicator with threshold score of 16.

^c.Value from Welch's t-test.

^d.Rosenberg Self-Esteem Scale.

^e.German Socio-Economic Panel external locus of control scale.

^f.Subscale of Clinical Perfectionism Questionnaire.