Why P/E ratios vary

The price/earnings ratios of four companies from the same industry are:
Company P/E Ratio
Ingles Markets  7.9
Kroger  6.6
Sprouts Farmers Market 18.3
Weis Markets 17.4
Source: Based on closing stock prices on March 17, 2019, and trailing-twelve-months earnings per share, both from Yahoo Finance.
Required:
What factors might explain the difference in the P/E ratios of these companies?