Financial services made up 3% of GDP in 1965, and that decade was a strong candidate for the greatest economic decade of the 20th century.

The checkable part is the factual figure that financial services made up 3% of US GDP in 1965. 'Greatest economic decade' is an opinion framed as a 'candidate', so only check that it is a defensible view (e.g. strong 1960s growth). True: BEA or standard historical data put the financial-services (finance and insurance) share of GDP in 1965 at about 3% (within ±0.5 percentage points). Mostly true: the share is within ±1 point on the measure nearest to Grantham's (e.g. 3.5–4%). Mixed: 3% matches only a narrow definition, while standard measures give 4–5%. Mostly false: standard measures are well above 3% (over 4.5%) and no reasonable definition gives about 3%, though the share was still far below its 2000s level. False: the 1965 share was nowhere near 3% on any measure (e.g. it was as high as later decades), or the 1960s were plainly weak economically.

Set before the research began.

1. E1 The Growth of Finance, In Graphs Center for Economic and Policy Research (CEPR) · 11 April 2016

   “During the 1940s to 1970s, finance typically accounted for about 3 to 4 percent of GDP; by 2005 and 2006, just before the financial crisis, finance claimed 7.6 percent of GDP.”

E1, an independent CEPR analysis, says finance typically made up about 3 to 4 percent of GDP from the 1940s to the 1970s, against 7.6 percent in 2005–2006. E1 gives no figure for 1965 itself, but 1965 falls within the period it describes, so a share typical of that period would be within about one point of Grantham's 3% figure [E1]. E1 gives no exact 1965 number, so it does not confirm the tighter ±0.5-point band needed for a full "true". The view that the 1960s were among the century's greatest economic decades is framed as opinion, and the evidence does not contradict it.