I searched for the phrase &quot;diminishing marginal returns&quot; but could not find it in the article which seems like a bit of an omission.<p>This is a fundamental economic concept - the more of something you have, the less value you derive from each incremental unit.<p>So, based on personal preferences, once you reach a certain level of income you will start to substitute away from labor (income) towards leisure&#x2F;free time (non-market activities such as hobbies, cooking, parenting, gaming, chilling).<p>The study data shows this pretty clearly (if I&#x27;m reading it correctly) - in Study 2b (wealthy people polled at a science museum) the median household income was $100-149k and the &quot;% Time Oriented&quot; was 69%. In Study 4 (online panel members who get free internet in exchange for survey participation) the median household income was $75-85k and the &quot;% Time Oriented&quot; was 46%.<p>The implied result that upper middle class folk are able to spend more time on leisure and are therefore happier on average than regular middle class folk doesn&#x27;t seem too groundbreaking.