How is productivity measured in their study though? As it's survey based I presume self reported? I worry that expectations may have a confounding effect: thos

How is productivity measured in their study though? As it's survey based I presume self reported? I worry that expectations may have a confounding effect: those required to work long hours may feel less productive relative to the higher expectations of their work culture? I could well believe they actually are less productive as well, on some objective scale, but not sure a survey could prove this.