Background Fibromyalgia is a pathology characterised by chronic pain that harms people's quality of life. This pathology requires an MRT that combines pharmacological and non-pharmacological treatments. Currently, FPAs are important to society not only by offering activities that improve fibromyalgia symptomatology but also by increasing public awareness of the disease. The present study compares the effectiveness of a multimodal rehabilitation treatment (MRT) with that of the activities of a fibromyalgia patient association (FPA), and identifies the patient characteristics that can interfere with the success of interventions.

Methods The quasi-experimental study selected forty-six older adults with fibromyalgia. The intervention group (n = 23) received pharmacological treatment, physical exercise, education, psychological therapies and Caycedian sophrology, while the control group (n = 23) carried out group psychological sessions and handicraft-based activities. Data collection included sociodemographic measures and responses to the Fibromyalgia Impact Questionnaire (FIQ). Participants were assessed pre- and post-intervention.

A descriptive analysis of the sociodemographic characteristics of the intervention and control groups was done. Qualitative variables were expressed as percentages, and quantitative variables were summarised as the median and interquartile range.

Shapiro-Wilk tests indicated that the dependent variables were not normally distributed (p < .05), so non-parametric statistical analyses were subsequently performed. The difference between the medians of the two patient groups was examined with the Mann-Whitney U test. Qualitative variables were compared with the chi-squared or Fisher's exact test, as appropriate.

Being a quasi-experimental study, without randomization of patients, the existence of initial pre-intervention differences in the dimensions evaluated by the FIQ scale between the two patient groups was tested with the Mann-Whitney U test. For the dimensions that showed significant pre-intervention group differences, the medians of the post- and pre-intervention differences between the two patient groups were tested. For those dimensions of the FIQ that showed no pre-intervention differences, the post-intervention values were compared. The changes in the FIQ score and its dimensions before and after the intervention in both groups were assessed using the Wilcoxon test.

Additionally, we carried out univariate and multivariate logistic regression analyses to identify the relationships between the independent variables studied and the improvement variable (increase, or not, of at least 8.1 points in the FIQ score after the intervention).

Finally, the sample was stratified by educational level (primary versus secondary/university studies) and age (younger than 60 years or 60+ years). The pre- and post-intervention scores were compared using the Mann-Whitney U test and the differences in each group were analysed with the Wilcoxon test.

Eligibility Criteria inclusion intervention group:

• to be diagnosed with FM
• to be between 18 and 80 years old
• be a patient of the unit care of FM
• the patients have to participate in nine of the treatment sessions
• the patients have to make the first visit in the unit care of FM during 2016

Eligibility Criteria inclusion control group:

• to be diagnosed with FM
• to be between 18 and 80 years old
• to be a member of the FM Patient Association of Terres de l'Ebre

Eligibility Criteria exclusion control intervention and group:

• not understanding Catalan or Spanish
• not providing correct contact data

The sample size was calculated on the basis of accepting an alpha risk of less than 0.05 and a beta risk of less than 0.20. The calculation indicated that 23 subjects each in the intervention and control groups were needed to detect a minimum clinically significant difference greater than or equal to 8.1 points in the FIQ score. A common standard deviation of 9.6 was assumed, and a rate of loss to follow-up of 0% was estimated, since there were no losses during sample recruitment.

The chosen standard deviation was that used by Lera (2009)