Not just small sample size, it's also biased. FTA, "The year-long experiment will compare two factions of municipal workers." Obviously, the results would be very different for various professions. For people who just push papers, yes they can be 25% faster to get 2 hours more with their family. However, what happens with the service industry? If the bus drivers work 2 hours less, then there will surely be less busses on the road.