Mendeley readership counts have been one of the most-studied altmetric indicators because of strong correlations with subsequent citations in many fields and because Mendeley's user base skews toward active researchers. Readership figures are available via Mendeley's API and are aggregated by altmetric providers. Limitations include uneven disciplinary coverage, the fact that readership reflects intent to read rather than quality of read, and the closed nature of the underlying data infrastructure (owned by Elsevier).
References
- Mohammadi E, Thelwall M 'Mendeley readership altmetrics for the social sciences and humanities' JASIST 2014. Altmetric Support documentation.