The FRS, or the ALS Functional Rating Scale helps patients keep track of their overall condition by measuring symptoms in all parts of the body: head, chest, arms, and legs.
A factor analysis was conducted on all of the questions in the ALSFRS-R. A factor analysis is used to measure correlations between the responses to a survey. A factor analysis of the items showed that 73% of total variance is clustered into four factors: fine motor, gross motor, bulbar, respiratory function.
The internal consistency of a scale refers to how well each component of the scale measures compared to the same underlying variable. This is measured by Cronbach’s alpha. Cronbach’s alpha can vary from 0.0 to 1.0. The value of Cronbach's alpha for the ALSFRS is 0.73 (raw) and 0.71 (standardized). All individual ratings were greater than 0.67.
The construct validity of a scale measures the extent to which the scale actually measures what you would like to measure. For the ALSFRS-R, this means that the investigators wanted to be certain that patients with lower scores on the ALSFRS-R actually had more severe disease than patients with higher scores. This was done by measuring the correlation between scores of the ALSFRS-R with the Sickness Impact Profile (SIP), and then comparing this to the previous correlation scores for the original ALSFRS with the SIP. The scores were almost identical (-0.72 versus -0.71, respectively). Also, the correlation between the ALSFRS-R and FVC% was compared to the correlation between the ALSFRS and FVC%. Again, the scores were nearly identical (0.41 versus 0.40, respectively). The test-retest variability was not assessed by the investigators.
|Domains||breathing, bulbar, chewing muscles, arms, mobility, lungs, Disease progression|
|Evaluated via ORE||No|
|License||Creative Commons Attribution - ShareAlike 3.0 United States|