Zero hours contracts in the UK. Are workers empowered or exploited

In the UK around 1 million workers have so-called zero-hours contracts. Does this mean that gig-economy workers are being exploited, or do they expand flexible working?

You can read more about this research and download the free DP:
Dolado, J, Lale, E and Turon, H. 2021. 'Zero-hours Contracts in a Frictional Labor Market'. CEPR