A code section was added to E:\project\vcdb3\Ranking.sql to explore city growth rates.
The main problem with estimating the average of <math>\frac{dollars_t - dollars_{t-1} }{dollars_{t-1}}<\/math>, where dollars is growth VC dollars invested in a citcity-year, is a truncation issue. <math>dollars_{t-1}<\/math> is often zero, and it is impossible for value to be below -100% while it can be above +100%.
I experimented with various ways to limit this issue, including considering:
*Only cities that have had more than $10m in a given year
*City-year pairs with more than $10m
*The top 100, 50 , or 20 cities in 2017, for years from 1990 to 2017 or 2000 to 2017.
*Only cities that had $10m or more for every year from 2000 to 2017
The growth rate for cities that had $10m or more for every year from 2000 to 2017 was 0.334 per year, implying that such "established" ecosystems double their VC every three years. There are 47 such cities. The list of average growth rates by city for these cities is below. The average growth rate increases to 39.17% for the 61 cities which have $10m or more for at least all bar one years, and to 51.43% for the 72 cities that have it fro for all bar two years.
city | avg