Patients and procedure
From June 2009 till March 2010, participants were recruited via the website of the Dutch Fibromyalgia Patient Association. Inclusion criterion was a self-reported diagnosis of fibromyalgia, confirmed by a doctor. If participants met this criterion, they were asked to complete an online questionnaire on mindfulness and theoretically related and unrelated constructs. Till August 2009, patients were asked if they were willing to complete the FFMQ for a second time. Patients who agreed received an email with a hyperlink to this second questionnaire, 2 weeks after completion of the first questionnaire.
Questions were included regarding age, gender, education (low: primary school, lower vocational education; intermediate: secondary school, intermediate vocational education; high: higher vocational training, university), disease duration and average pain intensity. The latter was measured on an 11-point numerical rating scale (NRS) ranging from ‘no pain’ (0) to ‘unbearable pain’ (10).
The FFMQ is a 39-item questionnaire that measures five facets of mindfulness: observe (8 items), describe (8 items), actaware (8 items), nonjudge (8 items) and nonreact (7 items) . Participants were asked to rate the degree to which several statements were true for them. Items were scored on a five-point Likert scale ranging from 1 (never or very rarely true) to 5 (very often or always true). Facet scores were computed by summing the scores on the individual items. Facet scores range from 8 to 40 (except for the nonreact facet which ranges from 7 to 35), with higher scores indicating more mindfulness. The Dutch FFMQ has shown adequate psychometric properties in meditating and psychology student samples (unpublished data).
Since the Dutch FFMQ has only been evaluated in highly educated people and in people with meditation experience, the questionnaire was first cognitively pretested in a clinical sample of 11 rheumatic patients to investigate the clarity of the wording of the items. In this pretest, patients filled in the FFMQ while they were thinking aloud. Afterwards, they were interviewed, using the three-step test-interview method , on the problems they perceived. Fourteen items (see Table 3) appeared problematic and each facet contained at least one problematic item. These items were partially rephrased by an experienced mindfulness psychologist without changing the content or meaning of the items. For example, ‘I criticize myself for having irrational or inappropriate emotions’ was changed to ‘I criticize myself for having illogical or inappropriate emotions’. And ‘I perceive my feelings and emotions without having to react to them’ was changed to ‘I perceive my feelings and emotions without having to do something with them’.
Acceptance and Action Questionnaire-II (AAQ-II)
The 10-item AAQ-II was used to assess the ability to accept aversive internal experiences, like negative emotions, thoughts and memories and to pursue goals in the presence of these experiences . Participants were asked to rate on a seven-point Likert scale the degree to which several statements were true for them. A total score, ranging from 10 to 70, was computed by summing the scores on the individual items. Higher scores indicate higher levels of general acceptance and less experiential avoidance. The Dutch AAQ-II has shown adequate psychometric properties . Internal consistency, expressed with Cronbach’s α coefficient, in our study was 0.88.
NEO Five-Factor Inventory (NEO-FFI)
Neuroticism (tendency to experience negative emotions) and openness to new experiences (proactive seeking and appreciation of new experiences) were measured using two scales of the NEO-FFI, a questionnaire addressing five core personality traits: neuroticism, extraversion, openness to experiences, conscientiousness and agreeableness [26–28]. Both the neuroticism and the openness to experiences scale consist of 12 statements. Participants were asked to rate the degree to which they agree with these statements. Each statement was rated on a five-point scale, yielding a scale score ranging from 12 to 60. Higher scores reflect higher levels of neuroticism or openness to experiences. The Dutch NEO-FFI has shown good psychometric properties . Cronbach’s α coefficients for neuroticism and openness to experiences in this study were respectively 0.91 and 0.77.
Toronto Alexithymia Scale (TAS-20)
The TAS-20 was used to assess alexithymia [29, 30]. The TAS-20 is a 20-item questionnaire containing three factors reflecting distinct facets of alexithymia: (1) difficulty in identifying feelings (7 items), (2) difficulty in describing feelings (5 items) and (3) externally oriented thinking (8 items). Items are scored on five-point scale, ranging from strongly disagree (1) to strongly agree (5). A total score was computed by summing the scores on all items. Total score ranges from 20 to 100 with higher scores indicating more alexithymia. The Dutch TAS-20 has shown good psychometric properties . Internal consistency of the TAS-20 in this study was satisfactory (Cronbach’s α = 0.83).
Hospital Anxiety and Depression Scale (HADS)
The HADS was used to measure the presence and severity of anxiety and depression symptoms . The HADS is a 14-item questionnaire comprising two subscales: the HADS-A (7 items) measuring anxiety and the HADS-D (7 items) measuring depression. Participants were asked to rate the degree to which they experienced several emotions in the past week. All items were rated on a four-point scale (0–3). Scale scores were computed by summing the scores on the individual items of a subscale. Scale scores range from 0 to 21 with higher scores indicating more symptomatology. The Dutch HADS has shown good psychometric properties . Cronbach’s α coefficients of the HADS-A and HADS-D in this study were respectively 0.88 and 0.86.
Short-Form 12-Item Health Survey (SF-12)
The SF-12, version 2, was used to assess mental and physical health . The SF-12 is a shortened form of the SF-36 and contains items on physical functioning (2 items), role limitations because of physical health problems (2 items), bodily pain (1 item), general health perceptions (1 item), vitality (1 item), social functioning (1 item), role limitations because of emotional problems (2 items) and general mental health (2 items). Norm-based physical component summary (PCS) and mental component summary (MCS) scores were calculated, ranging from 0 (poor well-being) to 100 (excellent well-being), with a mean of 50 and a standard deviation of 10 in the general population of the USA . The SF-12 has shown good psychometric properties [34, 36]. Internal consistency of the SF-12 in this study was satisfactory with a Cronbach’s α coefficient of 0.79 for both components.
Descriptive and standard psychometric analyses were performed using the statistical packages SPSS16. Missing values were imputed using the median value of an item (if no more than 10% of the items of a (sub)scale were missing). Given the normal distribution of the data, tested with Kolmogorov–Smirnov tests, parametric tests were used. Confirmatory factor analysis (CFA) was conducted with LISREL 8.70 (Scientific Software International, Lincolnwood, IL, USA). Missing values were imputed using the expectation-maximization algorithm procedure.
A CFA using the maximum likelihood estimation procedure was conducted to test the five-factor structure of the FFMQ. We first tested a correlated five-factor model. This model provided the best fit in the original validations of the FFMQ and assumes that the scale measures five distinct, but related, facets of mindfulness. The items were constrained to load on one factor only, error terms were not allowed to correlate and the variance of the factors was fixed to 1. Second, we tested a hierarchical five-factor model, in which the five factors were indicators of an overall mindfulness factor.
Besides the overall model chi-square statistic, where smaller values indicate better fit, multiple indices were used to examine the fit of the models. As suggested by Hu and Bentler , the non-normed fit index (NNFI), the comparative fit index (CFI), the standardized root mean square residual (SRMR), and the root mean square error of approximation (RMSEA) were used. NNFI and CFI values ≥0.90 and 0.95 were considered indicative of acceptable and good model fit, respectively. For the SRMR and RMSEA, values ≤0.10 and 0.08 and ≤0.08 and 0.06, respectively, were considered to reflect acceptable and good fit [38, 39].
Additionally, Pearson intercorrelations were computed between the five facets. Because the facets are assumed to measure related but distinct constructs, it was hypothesized that the facets should be significantly, but only moderately, correlated (r = 0.30–0.50).
Internal consistency and test–retest reliability
Internal consistency of the FFMQ facets was assessed with Cronbach’s α coefficients. Values above 0.70 were considered acceptable for research purposes . Test–retest reliability was assessed with intraclass correlation coefficients (ICCs) using a two-way random effects model and an absolute agreement definition. Single measures ICCs are reported. Values <0.40 were interpreted as poor, values between 0.40 and 0.59 as fair, values between 0.60 and 0.74 as good and values >0.75 as excellent .
Pearson correlation coefficients were calculated between FFMQ facets and other constructs, which were predicted to be moderately or strongly related (convergent validity) or weakly or not related (discriminant validity) to mindfulness. Correlations between 0.50 and 1.00 were interpreted as strong, correlations between 0.30 and 0.50 as moderate, correlations between 0.10 and 0.30 as small and correlations <0.10 as weak . Based on the content of the mindfulness facets and the other constructs, as well as the results of Baer et al. , predictions were made about the direction and strength of the correlations. Furthermore, predictions were made about which mindfulness facet(s) should most strongly correlate with each construct.
At least moderate and positive correlations were predicted between mindfulness facets (except observe facet) and acceptance (AAQ-II). Because acceptance includes the nonjudgmental acceptance of inner experiences, the strongest correlation was expected with the nonjudge facet. At least a moderate and positive correlation was also expected between the observe facet and openness to experiences (NEO-FFI), which includes the ability to be attentive to experiences. Similar to the results of Baer et al. , weak to small correlations were expected between openness to experiences and the other mindfulness facets (describe, actaware, nonjudge, nonreact). At least moderate but negative correlations were expected between mindfulness facets (except observe facet) and alexithymia (TAS-20). Alexithymia includes the difficulty to identify and describe feelings. Therefore, the strongest correlation was expected with the describe facet. At least moderate and negative correlations were also predicted between mindfulness facets (except observe facet) and neuroticism (NEO-FFI), anxiety (HADS-A) and depression (HADS-D). Previous studies [2, 16, 19] have shown that these psychological constructs/symptoms were most strongly correlated with the actaware and nonjudge facets. Therefore, the strongest correlations were expected with these facets. With regard to physical health (SF-12 PCS), weak correlations were expected with mindfulness facets. This construct does not seem to incorporate elements of mindfulness, neither reflects the absence of mindfulness.
Recently, Baer et al. have shown that the observe facet is sensitive to changes with meditation experience that alters its relationship with other variables [2, 19]. Only when internal and external experiences are observed mindfully, which is a skill that can be developed with practice, the observe facet acts like the other facets and is positively related with positive psychological functioning. Participants of this study were recruited via the website of the Dutch Fibromyalgia Patient Association. Generally, we do not expect a considerable amount of mindfulness experience in this study sample. Therefore, nonsignificant and weak correlations were expected between the observe facet and acceptance (AAQ-II), alexithymia (TAS-20), neuroticsm (NEO-FFI), anxiety (HADS-A) and depression (HADS-D).
Regression analyses (method forced entry) were conducted to examine whether the FFMQ facets contribute independently to the prediction of mental health (SF-12 MCS), depression (HADS-D) and anxiety (HADS-A), after controlling for differences in acceptance, alexithymia, neuroticism and openness to new experiences. In the first step, the five mindfulness facets were entered. In the second step, acceptance, alexithymia, neuroticism and openness to new experiences were entered.