Hi
I am looking for some advice regarding the appropriate code to use to assess agreement between 5 measurements taken in a single subject which results in correlated data. I am using Stata 14.
Individuals have had 5 separate measurements taken at different anatomical points along a blood vessel.
I have 40 such individuals.
I would like to see if there is a difference between the measurements in these individuals and the overall agreement between measurements.
My data is set up as: individual (1-40), site (1-5), measurement (continuous) with data in long form.

Through my reading, I came across a paper that did a similar analysis.
They state in their statistical methods: "The agreement between parameters describing the P, Pr and Px waveforms was summarised using the Intraclass Correlation Coefficient (ICC) function (Stata 13.1, StataCorp, Texas) derived from a linear mixed model analysis with participant as a random effect and location included as ordinal fixed effect rather than a continuous variable. This is appropriate to our data because the aortic sites were defined relative to anatomical locations, not measured distances."

In trying to replicate this, the code that I have used is:

mixed measurement site || id:

and then estat icc

I am wondering if:

1. This is the correct code for my question
2. Should i be using the expression i.site as it is a factor variable?

The regression output is attached below:

Array


In terms of interpreting the output, does this mean that the intercept is 0.5378991 (which is the grand mean) and that for each change in site as it moves from 1 to 5, there is a 0.0134852 increase at each site in the measurement outcome which is significant (p<0.001).

Thank you for your help
The link to the paper above is: https://www.ncbi.nlm.nih.gov/pmc/art...emss-73076.pdf

Best wishes
Nitesh