The "usefulness" of forward PR depends on 1) realistic growth and 2) politics. When the realistic / actual growth is above trend or accelerating, the corporate earnings are be more likely to beat investors' expectations which will lead to outperformance. In other words, multiple periods with different earnings growth profile requires to validate the usefulness of forward PE. Politics and business relationship have been a key driver on analysts' recommendation and hence earnings forecast of listed companies. The recommendations on corporates listed, especially in many emerging countries, tend to have more BUY than SELL. The reliability of earnings forward have been tinted by politics and business relation, not to mention we cannot predict the future.