The first levelling measurement is adjusted to the PS-InSAR measurements.
We introduced an arbitrary offset to the first levelling measurement to fit the PS-InSAR estimates of the time series to compare the relative variations between both techniques.
The first levelling measurements at the other sites began in October 2013.
At a first level, the unobserved disease process (Markov model) was introduced and at a second level, the measurement process was modeled, making the link between the unobserved disease states and the observed biomarker values.
The second level of measurement invariance is known as metric [ 45, 50] or weak [ 52] invariance and it pertains to the invariance of factor loadings across groups and, in a longitudinal perspective, over time.
The third level of measurement invariance is scalar [ 45] or strong [ 50, 52] invariance.
The OIDP focuses on the third level of measurement, thus assessing oral impacts on the ability to perform daily activities.
The fourth level of measurement invariance entails the equivalence of the residual variances, for continuous items, and of scale factors, for ordinal items.
The first level of measurement invariance is configural invariance, which implies that the same factor structure holds for all six groups, but parameter estimates may vary across groups.
Tabachnick and Fidell (2007) stated that for sufficient power to discover cross-level effects, we need at least 20 measurements at the second level, with a minimum of three measurements at level 1.
In the multilevel analyses we consider location as the first level, patient as the second level, and the three measurements as a third level, using the principles of Twisk [ 45].
