This study used a new sample of fibromyalgia patients to confirm the factorial structure of the ICAF obtained by the previous study . Therefore, it confirms the results obtained as well as the precise reference values to calculate the T scores, as reflected in the Additional File 1. Said Additional File 1 also includes the ICAF, as well as the correction guidelines, in light of the original study data.
The study of the scientific integrity of the instrument was also completed, offering satisfactory data with regard to its test-retest reliability, the internal consistency of the different factors included in the ICAF, as well as its sensitivity to change. The total score of the questionnaire, as well as the scores for the emotional, physical and active coping factors all varied with statistical significance after conventional medical treatment.
There was not a statistically significant change in the passive coping factor. It should be mentioned that in the previous study , the greatest score in the passive coping factor was characteristic of poorer physical shape, measured by the 6-minute walk test . Recently, Karsdorp and Vlaeyen  found that fibromyalgia patients who refrain from physical activity and seek help (asking for assistance) to control their pain are characterised by greater severity and disability. It is possible that the changes in coping strategies, and particularly the passive strategies, require longer periods of intervention and evaluation. The pain-avoidance factor (passive pain-coping) is particularly relevant to determine a risk of longer aggravated distress in fibromyalgia . It is reasonable that the change score for passive coping is higher (0.8391) than in the other factors. This implies that the minimal score change (1 SEM) in this factor should also be higher than in the others factors and corresponds well with the level of distress associated with passive coping . This should be dealt with through therapeutic intervention studies that have a longer duration, using psychological treatment and physical exercise.
The results obtained in passive coping must be considered in relation with gender. In FM studies female percentages are about 95% or more [32, 33], which indicates that there is an influence of specific gender differences in pain perception, specifically in coping with pain. Women report more pain than men , and men use more active coping than women . It is likely that female FM patients may have more difficulties to reduce passive coping and to increase active coping.
The ICAF scores in patients and controls show large differences, both regarding the overall score and each of the four factors, which emphasises the specificity of ICAF for fibromyalgia patients. This is especially pronounced both active and passive coping factors. The control subjects do not have symptoms that interfere with their lives, namely pain, and thus it clearly makes no sense to discuss coping strategies.
The differences are still more evident on the physical scale, in which the mean patient score is four times that obtained with the controls (see Table 3).
All these data show the instrument's capacity to differentiate between the two population groups.
Therefore, the ICAF has a set of domains relevant to fibromyalgia and it largely responds to the need mentioned by several authors: to have an extensive set of measures for the syndrome that can be used in both clinical trials  and in daily clinical practice. The ICAF was developed and compared to physical functionality tests, encompassing the domains in which there was the greatest consensus at OMERACT 9 .
This instrument also includes the evaluation of emotional aspects such as depression and anxiety. The latter is known as a domain of interest for research, as distress may contribute to increasing the importance of the painful points characteristic of the ACR classification.
One of the inconveniences of the ICAF may be its length, given that it includes 59 items, compared to most of the tools used for FM patients. However, if we consider that to obtain the same information collected by the ICAF, several different tools must be used together, adding up into many more items, we can conclude that the ICAF saves a considerable amount of time for both the doctor and the patient. The average time that the patient needs to fill the ICAF is 15 minutes.
The ICAF shows well balanced information about the main areas of severity in FM. Some scales have a small but clinically significant relevance, such as passive coping, while the remaining scales, as well as global score, are very useful for understanding the clinical situation of the patient and for starting up with treatment.
In relation with the length of the ICAF, it is possible that future studies may reduce the number of items preserving the information offered.
The fact that this study was conducted in Spain may be a limitation to generalize ICAF to other patients in different countries. This limitation may affect the ICAF structure but not the items because they were selected from well-known instruments validated in most countries .