We could search for 'ROI of ycombinator investments' and find valuation numbers from a number of years ago.
From the first page of search results, we'd then learn about "return on capital" and how the standard YC seed terms have changed over the years.
Return on capital: https://en.wikipedia.org/wiki/Return_on_capital
From the See also section of this Wikipedia page, we might discover "Cash flow return on investment" and "Rate of return on a portfolio"
From the "rate of return" Wikipedia page, we might learn that "The return on investment (ROI) is return per dollar invested. It is a measure of investment performance, as opposed to size (c.f. return on equity, return on assets, return on capital employed)." and that "The annualized return of an investment depends on whether or not the return, including interest and dividends, from one period is reinvested in the next period. " https://en.wikipedia.org/wiki/Rate_of_return
From the YCombinator Wikipedia page, we might read that "The combined valuation of the top YC companies was over $155 billion as of October, 2019. [4]" and that "As of late 2019, Y Combinator had invested in >2,000 companies [37], most of which are for-profit. Non-profit organizations can also participate in the main YC program. [38]" and then read about "seed accelerators" and then "business incubators" in search of appropriate metrics for comparing VC performance. https://en.wikipedia.org/wiki/Y_Combinator
ROI is such a frou frou statistic anyway. What does that even mean, ROI? In any case, YC itself is not a public company, per se, AFAICT, so, it's not so easy as going to https://YCharts.com, entering the equity symbol, clicking on "Key Stats", and scrolling down to "Profitability" to review [Gross | EBITDA | Operating] [Profit] Margin.
The LTSE (Long-Term Stock Exchange) is where people who are in this for real are really doing it now.
