Measurement invariance of the WHOQOL-AGE questionnaire across three European countries - Santos D., Abad F.J., Miret M., Chatterji S., Olaya B., Zawisza K., Koskinen S., Leonardi M., Haro J.M., Ayuso-Mateos J.L., Caballero F.F. (Quality Of Life Research, 2018)