Table 1.

General characteristics of 23 included studies

Reference	Place of study	Targeted population (general population if not specified)	N	% Male	Mean age
Scheeres 2009 [18]	The Netherlands	Chronic fatigue syndrome	226	26.1%	37.0
Kaleth 2010 [33]	USA	Fibromyalgia patients	30	10.0%	49.1
Lachat 2008 [35]	Vietnam	Grade-11 students	227	NA	16.0
Mader 2006 [36]	Switzerland	German-speaking	35	62.9%	54.7
Dinger 2006 [25]	USA	College students	123	26.0%	20.8
Ekelund 2006 [31]	Sweden		185	47.0%	41.8
Vandelanotte 2005 [29]	The Netherlands		53	NA	NA
Craig 2003 [17]	12 countries		716	49.2%	37.3
Wolin 2008 [39]	USA	African-Americans	142	35.9%	44.0
Rangul 2008 [23]	Norway	Secondary school students	67	44.8%	14.9
Kurtze 2008 [39]	Norway	Men, age 20-39	108	100%	32.4
Macfarlane 2007 [19]	Hong Kong, China		49	61.2%	28.7
Faulkner 2006 [32]	Canada	Schizophrenia patients	35	63.0%	39.7
De Cocker 2009 [30]	Belgium		288	48.3%	38.7
Deng 2008 [20]	Guangzhou, China		224	33.9%	65.2
Cust 2009 [40]	Australia		177	NA	NA
Timperio 2004 [42]	Australia		285	NA	NA
Kolbe-Alexander 2006 [43]	South Africa		42	41.0%	66.8
Papathanasiou 2010 [37]	Greece		218	51.8%	23.0
Ramirez-Marrero 2010 [38]	Puerto Rico	Hispanic patients with HIV	58	60.3%	46.5
Ishikawa-Takata 2008 [28]	Japan		150	49.3%	38.7
Egeland 2008 [44]	Canada	Cree Territory	161	59.0%	38.4
Fogelholm 2006 [41]	Finland	Finnish Defence Forces	967	100%	29.0