Last year, I ran across an article analyzing whether high altitudes matter in South American international soccer. The authors run regressions with the away team’s altitude change as an explanatory variable and find that climbing but especially descending hurts the away team. Descending 2,000 meters seems to lower away team winning percentage by over 10 points. Pretty surprising finding.
However, these regressions only control for home team quality. It just so happens that Bolivia, Ecuador, and Colombia (i.e., the descending teams) are historically weak teams. What we have here is omitted variables bias — the naive analysis implies that descending harms performance, when in reality descending teams just aren’t very good.
On my quest for causation, Continue reading