the dirt-in-your-food index

I prefer the food at the Rwandan buffet across the street to the one a block away, largely because I'm less likely to crunch down on dirt in any given bite.

Before coming here I never thought that the probability of eating dirt would be an important metric for choosing a restaurant. But here's what I can't figure out: the restaurant across the street (low dirt-in-your-food index) is less expensive than the one down the street (high dirt-in-your-food index).

Which means that other people don't care about the dirt-in-your-food index. They're using other indices. Maybe the relevant index is rice-isn't-burned or beans-don't-smell.

Either way, I've got a lot to learn about Rwandan markets.