Table I.

Included studies: Patient-related phenomena associated with sick leave.

First author, year, country [reference]	Aim	Study design	Patient-related phenomena	Quality of paper
Harris, 2009, Boston, US [30]	A comparison of somatizing and non-somatizing patients regarding disability and role impairment, and determination of the independent contribution of somatization to this	Cross-sectional observational study with self-report questionnaires (n =467)	Somatizers reported more often psychiatric comorbidity (60% vs. 14%) and somatic co morbidity (39% vs 30%) than non-somatizers, and also more often reported work limitations (OR 3.2)	S
Muller, 2008, South Africa [34]	To evaluate the prevalence of depressive and anxiety disorders in patients with multisomatoform disorder, and to compare demographic and clinical outcomes in those with and without comorbidity	Cross-sectional observational study with structured diagnostic interview (n =51), 90% females. Among outcomes were disability and reported sick-days	4 or more psychiatric comorbid disorders were associated with significantly higher levels of overall disability, p =0. 041	M
Hoedemann, 2009, Netherlands [32]	To assess the prevalence of MUPS in sick-listed employees and its associations with depressive or anxiety disorders, health anxiety, distress, and functional impairment	Cross-sectional observational study (n =489)	A prevalence of 15.1% severe MUPS, i.e. >15 symptoms on PHQ-15, which was associated with 4–6 times more psychiatric comorbidity and impairment	S
Gureje, 1997, Australia – WHO, 14 countries [29]	To determine the frequency and correlates of somatization in primary care settings in 14 countries	Cross-sectional study with a stratified sample (n =5438). Correlates: gender, age, physical health and disability	Somatization is common across cultures and it is associated with older age, less education, worse self-reported health, psychiatric comorbidity, and more occupational disability (more than >1 day self-reported last month)	M
Gullbrandsen, Norway, 1998 [28]	To describe the prevalence of self-perceived work disability in general practice and the level of psychosocial problems among work-disabled patients.	Cross-sectional observational study (n =1058). Self-reporting questionnaire	Study identified 7 not work-related psychosocial problems of which 6 were 2–3 times more likely to occur among the work-disabled patients, indicating a correlation between greater self-reported work disability with increasing number of psychosocial problems	S
Hoedemann, 2010, Netherlands [31]	To compare patients with high levels of somatic symptom severity (HLSS) vs. lower levels. Outcomes: duration of sick leave, return to work and disability	Cross-sectional observational study with the same population as in reference [32]	Patients with HLSS had longer duration of sick leave (median 78 days longer) and remained more often disabled. Health anxiety and older age were associations for sick-leave duration among HLSS patients	S
Kroenke, US, 2002 [33]	To validate a 15-item questionnaire on mental and somatic symptoms and its association with functional status, disability days, and health-care utilization	Cross-sectional observational study (n =6000). Outcomes included functional status (SF-20), self-reported sick days and clinic visit	Greater levels of somatization severity were associated with a stepwise increase in disability days	S
Al-Windi, 2005, Sweden [27]	To examine the impact of different symptoms on health-care utilization	Cross-sectional observational study (n =1055). 7 symptoms groups: depression, tension, GI, musculoskeletal, metabolism, cardiopulmonary, and head	A linear correlation between numbers of symptom categories and days of sick leave	M
Thorslund, 2007, Sweden [25]	To determine the effect of solution-focused group therapy on RTW among MUPS1 patients on long-term sick leave	RCT (n =30). Sick-listed for 1–5 months. Randomized to solution focus group therapy or waiting list (control)	The intervention group returned to work at a significantly higher rate and worked more days, and this difference increased at 3-month follow-up	M
Roelen, 2010, [18], Netherlands	To estimate prevalence of Subjective Health Complaints (SHC), and see if either number or type of complaints were related to sickness absence	Cross-sectional observational study (n =409). Self-reported questionnaire, linked to number of sickness absence episodes in 2003–2004	Prevalence of SHC: 78%. Positive relation between number of SHC and number of sickness absence episodes	S

Note: ¹Redefined as MUPS in this study: Diagnoses fell into two categories, D4 (depression, anxiety, stress-syndrome, and adjustment reactions) and D12 (musculoskeletal illnesses and fibromyalgia).