Evaluative frailty index for physical activity (EFIP): a reliable and valid instrument to measure changes in level of frailty.

Background: Physical activity is assumed to be important in the prevention and treatment of frailty. It is unclear, however, to what extent frailty can be influenced because instruments designed to assess frailty have not been validated as evaluative outcome instruments in clinical practice.

Objectives: The aims of this study were: (1) to develop a frailty index (i.e., the evaluative frailty index for physical activity [EFIP]) based on the method of deficit accumulation and (2) to test the clinimetric properties of the EFIP.

Design: The content of the EFIP was determined using a written Delphi procedure. Intrarater reliability, interrater reliability, and construct validity were determined in an observational study (n=24).

Method: Intrarater reliability and interrater reliability were calculated using Cohen kappa and intraclass correlation coefficients (ICCs). Construct validity was determined by correlating the score on the EFIP with those on the timed "up & go" test (TUG), the performance-oriented mobility assessment (POMA), and the Cumulative Illness Rating Scale for Geriatrics (CIRS-G).

Results: Fifty items were included in the EFIP. Interrater reliability (Cohen kappa=0.72, ICC=.96) and intrarater reliability (Cohen kappa=0.77 and 0.80, ICC=.93 and .98) were good. As expected, a fair to moderate correlation with the TUG, POMA, and CIRS-G was found (.61, -.70, and .66, respectively).

Limitations: Reliability and validity of the EFIP have been tested in a small sample. These and other clinimetric properties, such as responsiveness, will be assessed or reassessed in a larger study population.

Conclusion: The EFIP is a reliable and valid instrument to evaluate the effect of physical activity on frailty in research and in clinical practice.