LKY ruled from 1959-1990. Singapore's GDP over that time grew at a 14% compound annual growth rate: https://www.macrotrends.net/countries/SGP/singapore/gdp-gros....
--which gives a rate of growth of 10.7%, and some of that will be inflation: the data is denominated in USD, which famously inflated rapidly in the late 1970s and early 1980s.
Here is my math: solve for rate where e ^ (31 times rate) = 11828 / 428. (I am compounding continuously.)
ADDED. according to https://www.bls.gov/data/inflation_calculator.htm, the dollar inflated by a factor of 4.39 between 1959 and 1990, giving an inflation-adjusted rate of 5.93%.
I wonder what South Korea's economy did during those years.
https://data.worldbank.org/indicator/NY.GDP.MKTP.KD
Over the 29 years 1960-1989, Botswana experienced the greatest growth at 11.6%/year, followed by South Korea at 9.6% and Singapore at 8.6%. World growth was 4.1%, and U.S. growth was 3.6%. The worst performer was Guyana at 0.6%. (This among only those countries with available data at the start and end years.)
The same comparison for the period 1990-2019 shows top performer Equatorial Guinea at 15.0%/year, followed by China at 9.5%. Singapore weighed in at 5.6%, the World at 2.8%, and the U.S. at 2.5%. Bottom performer was Ukraine at -1.4%, and second-worst was Georgia at 0.2%. Former bottom performer Guyana faired much better at 3.8%.
Population does not cause GDP. Adjusting for population will give a better idea of changes in living standards but won't explain the differences in economic growth.
Population density may be related to economic growth, and for this reason it may be misleading to compare Singapore, which is essentially a city-state, to nation-states.
Singapore's per capita GDP was close to double South Korea's in 1990, though its divorce from Malaysia was less messy than the Korean War.