Issue on page /23-Challenges-with-Effect-Heterogeneity-and-Nonlinearity.html

[fclerot]

typo :

"For example, pretend for a moment that your experimental data actually looks like the following plot, where you test higher prices for the segment A (rich population) but only lower prices for the A population."

should be

"For example, pretend for a moment that your experimental data actually looks like the following plot, where you test higher prices for the segment A (rich population) but only lower prices for the B population."