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Last week I discussed U-shaped relationships, and how to test for them. This week, I would like to discuss higher-order nonlinear relationship, or relationships that are “more nonlinear” than U-shaped relationships.

There are many ways one can approach the estimation of nonlinear relationships. I will focus only on a handful of them in this post, from least to most nonlinear, and from semiparametric to nonparametric.

A good first step beyond the estimation of a U-shaped relationship would be to estimate the equation

I cannot remember how or where I came across this stuff, but this site has a number of cheatsheets for Stata, covering topics as diverse as basic data processing, data transformation, visualizing your data, customizing data visualizations and, obviously, data analysis.

I’ve been using Stata since 1999, and I managed to learn quite a bit from looking at those cheatsheets.

ht: Jesse Tack.

About a month ago, I was interviewed by Jeremy Cherfas for the Eat This podcast for an episode on the economics of quinoa.

The end result is an extremely well-researched episode titled “It Is OK to Eat Quinoa” which also features my coauthor Seth Gitter, UC Berkeley graduate student Andrew Stevens, and a few others who know a lot about quinoa. The episode’s main page is here, but you can also listen directly by clicking here.