In Norway, workers at codetermined firms have higher wages and less earnings risk, though the causal mechanism appears to be the size and unionization of codetermined firms, rather than worker representation.
"We find that a worker is paid more and faces less earnings risk if she gets a job in a firm with worker representation on the corporate board. However, these gains in wages and declines in earnings risk are not caused by worker representation per se. Instead, the wage premium and reduced earnings risk reflect that firms with worker representation are likely to be larger and unionized, and that larger and unionized firms tend to both pay a premium and better insure workers against fluctuations in firm performance. Conditional on the firm’s size and unionization rate, worker representation has little if any effect."
empirical