The complete article "A psychometric study found AMSTAR 2 to be a valid and moderately reliable appraisal" can be downloaded at the website of the "Journal of Clinical Epidemiology", Volume 114, pp. 133-140 (charges may apply).
R. C. Lorenz, K. Matthias, D. Pieper, U. Wegewitz, J. Morche, M. Nocon, O. Rissling, J. Schirm, A. Jacobs:
A psychometric study found AMSTAR 2 to be a valid and moderately reliable appraisal.
in: Journal of Clinical Epidemiology, Volume 114 2019. pages 133-140, DOI: 10.1016/j.jclinepi.2019.05.028