What the Treynor ratio measures
Unlike the Sharpe ratio, which penalises all volatility, the Treynor ratio only considers systematic risk (beta). This makes it the appropriate performance metric for portfolios that are part of a larger diversified allocation, where idiosyncratic risk is irrelevant.
Higher Treynor ratios indicate better compensation per unit of market risk taken. A negative Treynor ratio means the portfolio underperformed the risk-free rate.