The Mental Health Continuum-Short Form (MHC-SF) measures positive mental health and comprises 14 items, representing various feelings of well-being. Respondents rate the frequency of every feeling in the past month on a 6-point Likert scale (never, once or twice a month, about once a week, two or three times a week, almost every day, every day). The MHC-SF contains three subscales: emotional, psychological and social well-being. MHC-SF has shown high internal and moderate test-retest reliability, convergent and discriminant validity.

The TIC-P generates quantitative data about direct medical costs and indirect societal costs as a consequence of psychological/psychiatric illnesses.

To measure the quality of the health status of cancer patients a validated health-related quality of life (HRQoL) instrument will be used, the EuroQol-5D (EQ-5D). This HRQoL instrument will be completed by the patient together with a researcher and is available in a validated Dutch translation (Lamers, 2005). The EQ-5D is a generic HRQoL instrument comprising five domains: mobility, self-care, usual activities, pain/discomfort and anxiety/depression. The EQ-5D index is obtained by applying predetermined weights to the five domains. This index gives a societal-based global quantification of the participant's health status on a scale ranging from 0 (death) to 1 (perfect health). Participants will also be asked to rate their overall HRQoL on a visual analogue scale (EQ- 5D VAS) consisting of a vertical line ranging from 0 (worst imaginable health status) to 100 (best imaginable).

In addition to the EQ-5D, the SF-12 will be administered for explorative purposes for there are indications that the SF-12 is more sensitive for changes in HRQol in populations with less severe morbidity (Johnson and Coons, 1998).

The 39-item Five Facet Mindfulness Questionnaire has been developed as a reliable and valid comprehensive instrument for assessing different aspects of mindfulness. A Dutch 24-item short form of the FFMQ (FFMQ-SF) was developed and assessed in a sample of 376 adults with clinically relevant symptoms of depression and anxiety and cross-validated in an independent sample of patients with fibromyalgia. Confirmatory factor analyses showed good model fit for the five-factor structure of the FFMQ-SF: observing, describing, acting with awareness, nonjudging, and nonreactivity. The FFMQ-SF was related to measures of psychological symptoms, well-being, experiential avoidance, and the personality factors neuroticism and openness to experience.

The rumination subscale of the RRQ assesses a neurotic self-attentiveness (i.e. recurrent, primarily past-oriented thinking about the self), which is prompted by threats, losses, of injustices to the self. Subjects rate their level of agreement of disagreement on a five-point rating scale (e.g., "I always seem to be rehashing in my mind recent things I've said or done"). There is evidence of good internal consistency (.90) and stability over a 10-month period and convergent validity. The measure in the current study was translated into Dutch using the guidelines of the International Test Commission (Hambleton, 1994). Cronbach's alphas were .88 and .90 in Sample 1, and .90 and .91 in Sample 2, respectively (Luyckx et al., 2008).

Personality is measured with the NEO Five Factor Inventory (NEO-FFI, Costa & McCrae, 1992) which consists of five domains: neuroticism, extraversion, openness, altruism, and conscientiousness.

The Mindful Attention Awareness Scale (MAAS) will be administered before each MBCT session to assess mindful attention in daily life

We will examine self-reported individual group cohesion ratings during the MBCT training with a Dutch Group Cohesion Questionnaire that has been used in cancer patients before (May et al., 2008). The GCQ-23 uses 22 items across four scales: the bond with the group as whole, the bond with other members, cooperation within the group and the instrumental value. Each item is rated from 1 (totally disagree) to 6 (totally agree). Internal consistency of all scales was reported to range from adequate to good (0.66-0.88).

The Working Alliance Inventory (WAI) is most often used to assess working alliance between participant and healthcare professional. We will use the Dutch translation of the short form (WAI-S, Vervaeke & Vertommen, 1996), which is closely related to the original scale and also has good psychometric and predictive quality (Busseri & Tyler, 2003). The WAI-S is a 12 item, self report questionnaire, rated on a 7-point Likert scale (1 = never to 7 = always) with three subscales: 1) agreement between participant and therapist on the goals of the therapy; 2) agreement on the rationale of the therapy addressing the problems of the participant; and 3) the quality of the interpersonal bond between the participant and the therapist.

In the current study, positive and negative affect is assessed before each MBCT session using the International Positive and Negative Affect Scale - Short Form. The cross-sample stability, internal reliability, temporal stability, crosscultural factorial invariance, and convergent and criterion-related validities of the I-PANAS-SF were examined and found to be psychometrically acceptable (Thompson, 2007).

Hospital Anxiety and Depression Scale - anxiety and depressive symptoms at follow up.