Employer ratings on review sites are inevitably influenced if not directly driven by business performance - it’s easy to score high when the market is soft and the money is rolling in. Ratings over time through various economic up and downturns might be interesting, something which
Culturama seem to be trying to do. Nevertheless,
this report by Glassdoor is not without value, particularly as it remains a heavily used site for job seekers seeking validation. US data, with cool drop downs and filters.