The statistic, quoted by David Brooks in the review, says that "For every 10 percent reduction in population density, the odds that people will join a local club rise by 15 percent."
Steuteville does the math: "So let's start at 11,000 people per square mile, which is approximately the population density of Eastern US cities like Boston and Philadelphia. Now ratchet that on down, in 10 percent density reductions, to the average population of a typical large suburb, 1,600 people per square mile. Brooks's formula nets an increase of more than 1,100 percent in local club membership! If you take it further, to 700 people per square mile, the density of many exurban communities, club membership is up 3,300 percent from the figure for Boston. Wow! Those people must join a whole lot of clubs! How do they find the time with all of the commuting that they do?"