Development of the HRQoL scale consists of item selection phase and validation phase. The first one is usually based on correlation matrix analysis and factor analysis (FA), which let to exclude overlapping items, and those which may contribute to scores of several latent variables measured by the scale [8]. Validation phase leads to confirmation of validity and reliability of the scale [9]. Validity is being proved by showing scales' relationhip with other tools measuring the same latent variables as the scale, and other variables which should be related to those of interest [10]. Reliabilty is confirmed by assessment of the scale's and its items' properties in terms of classical test theory (CTT) or item response theory (IRT) [11]. This methodology may be not sufficient - as concernes development phase - in case of rare diseases, when sample size demanded by FA may not be provided. The impact methodology was developed to deal with this requirements, but selecion of the items in its case is based on different item characteristics than that which is further used in the studies using the developed tool [12]. To develope CHVAQoLS we conducted multistage procedure in which FA was used with respect to particular item sets (called domains) to provide unidimensionality of subscales constituting the scale, and analysis of multidimansionality of the scale was conducted by indirect method using multi-trait matrix [13]. Such methodological approach required repetition of some stages of development procedure and was in details described in [1].