Table 2.

Familial and genetic influences for chronic widespread pain and fibromyalgia.

Pain context	Type of study	Population or clinic	Number of participants	Multivariate analysis	Reference	Overall quality∗
CWP	Twin study	Population	44,897	No	Kato et al. [37]	+++
CWP	Twin study	Population	926	Yes	Burri et al. [38]	++++
CWP	Twin study	Population	8564	Yes	Vehof et al. [39]	+++
CWP	Twin study	Population	2256	Yes	Malkin et al. [40]	+++
CWP	Prospective population cohort	Population	6589	Yes	Zadro et al. [41]	++++
CWP	Review	N/A	N/A	N/A	Kerr and Burri [42]	N/A
FMS	Family study	Clinic	805	Yes	Arnold et al. [43]	++
FMS	Review	N/A	N/A	N/A	Park et al. [44]	N/A

^∗Overall quality:  + , very low;  ++ , low;  +++ , moderate;  ++++ , high.