Several more valid and reliable instruments are employed by researchers internationally to measure HRQoL, like the SF-36 and the shorter version SFv-IZ. Because the NHP instrument was used at the baseline of the study, it made sense to use it later to enable comparisons. When the study was initiated in 1995, HRQOL research was a new field. During the past 10 years, this field has grown remarkably, and there are new instruments available that have been developed, tested, and validated for the Finnish culture. However, it was not possible or feasible to change the instrument after the study began.