The Historical Evolution of Attempts to Complement or Replace the Price–Earnings Ratio (P/E) through the Introduction of Earnings Growth, Interest Rates, and Risk in Equity Valuation

The Price–Earnings ratio (P/E) has long occupied a central position in equity valuation, yet it remains a fundamentally static indicator that does not explicitly incorporate earnings growth, the time value of money, or risk. This article retraces the historical evolution of analytical frameworks that have sought to correct, extend, or surpass the P/E ratio by progressively introducing these missing dimensions.

From traditional valuation multiples to discounted cash flow models and growth-adjusted ratios, the literature reveals a gradual conceptual shift. The Gordon–Shapiro framework demonstrates that growth and discounting are already embedded in the P/E ratio, but in an implicit and non-invertible form, which limits its economic interpretability and operational usefulness. Parametric adjustments to the P/E ratio, such as the PEG or the GA-P/E, partially improve the treatment of growth, yet fail to make time an explicit variable of valuation.

A decisive step is reached when valuation begins to be formulated in terms of payback time, first with the Payback Period introduced in 1984, and later through its academic formalization in the Break-Even Time. The conceptual break occurs with the Potential Payback Period (PPP), which generalizes these approaches by making time the explicit output of valuation, while simultaneously rendering growth and discounting assumptions explicit.

Within this framework, the P/E ratio appears as a static special case of the PPP, corresponding to a situation with neither growth nor discounting. This generalization property shows that the limitations of the P/E ratio can be overcome by construction, without sacrificing its interpretative simplicity. Time-based valuation can ultimately be translated into equity returns, through the Stock Internal Rate of Return (SIRR) and its extension including price appreciation, SIRRIPA, offering a coherent and unified framework for the analysis of equity value and returns.