The Treynor Ratio is similar to the Sharpe Ratio but substitutes Beta (systematic risk) for standard deviation. This measures the excess return earned for each unit of market risk taken on, completely ignoring idiosyncratic (asset-specific) risk.
It is primarily used to evaluate fully diversified portfolios where idiosyncratic risk has been mostly eliminated. If a portfolio is perfectly diversified, Sharpe and Treynor give identical rankings.
A higher Treynor ratio indicates better performance relative to market beta exposure. In active management, it helps identify whether a manager is actually adding value or simply taking on amplified market risk.