Table 3.

Between-group differences for the secondary outcomes Patient Health Questionnaire (PHQ-4) and the Brief Illness Perception Questionnaire (IPQ) from the second sample

Variable	COVID period group (n = 313)	Reference period group (n = 222)	Standardized mean difference	p value
PHQ-4 total score, median (IQR)	0 (0 to 1)	0 (0 to 1)	0.11	0.14
PHQ-4 subscale anxiety, median (IQR)	0 (0 to 0)	0 (0 to 1)	0.09	0.28
PHQ-4 subscale depression, median (IQR)	0 (0 to 0)	0 (0 to 0)	0.12	0.11
IPQ consequences: How much does your illness affect your life? (10 = severely affects my life), median (IQR)	4 (2 to 7)	4 (1 to 7)	0.048	0.79
IPQ timeline: How long do you think your illness will continue? (10 = forever), median (IQR)	5 (3 to 8)	6 (3 to 8)	0.03	0.24
IPQ personal control: How much control do you feel you have over your illness? (0 = absolutely no control), median (IQR)	6 (4 to 8)	6 (5 to 8)	0.01	0.91
IPQ treatment control: How much do you think your treatment can help your illness? (10 = extremely helpful), median (IQR)	8 (5 to 9)	8 (6 to 9)	0.15	0.03
IPQ identity: How much do you experience symptoms from your illness? (10 = many severe symptoms), median (IQR)	3 (1 to 6)	4 (1 to 7)	0.16	0.14
IPQ concern: How concerned are you about your illness? (10 = extremely concerned), median (IQR)	3 (1 to 6)	3 (1 to 7)	0.14	0.37
IPQ coherence: How well do you feel you understand your illness? (10 = understand very clearly), median (IQR)	9 (7 to 10)	9 (7 to 10)	0.008	0.35
IPQ emotional representation: How much does your illness affect you emotionally? e.g. does it make you angry. scared. upset or depressed? (10 = extremely affected emotionally), median (IQR)	1 (0 to 5)	2 (0 to 5)	0.22	0.02
IPQ total score, mean (SD)	28.5 (15.3)	29.9 (15.9)	0.09	0.62

Reported values per group are medians plus interquartile range (IQR) or means plus SD; in addition, the unadjusted standardized mean difference and the p values for the adjusted group factor from the linear mixed model analyses are shown.