Equity Valuation Doubt long, sales, statements, companies, following

LorrinCFA

Please explain the following statements regarding interpreting the P/E multiples and  P/CF multiples  and price to sales multiples…..
1) According to empirical research,differences in P/E ratios are significantly related to long term stock returns
2) differences to P/ CF ratio overtime are related to differnces in long term avg returns on stocks…
3) Using P/S ratio does not reflectthe differnces in cost structure and operating effiency between companies…
Thanks