Table 2.

Zip code fixed-effects linear probability regression estimates for the relationship between casino slot machines per capita and large-for-gestational-age births among Native Americans, 1987-2011 (N=124 zipcodes; n=21011 births)^a,b,c,d

	β (95% confidence interval)
Casino slots per capita	−0.13 (−0.25, −0.01)*

^aThe coefficient is estimated using a zip code fixed-effects linear probability regression model for large-for-gestational-age births (LGA). The model includes an indicator variable for each year (centred at the baseline year) to account for secular trends and controls for maternal age, child sex, gestational age in days and parity. Results were multiplied by 100 so that the coefficient presented is interpreted as the percentage point change expected. Robust clustered (at the zip code level) standard errors were used.

^bSlots per capita refers to the total number of casino slot machines in a zip code divided by the total number of Native Americans living on tribal lands in that zip code, using the average population between 1990 and 2010 from the US Census so that the denominator does not change.

^cRace was self-reported on the birth certificate. For years allowing multiple race identifications (2000-11), we included newborns from women or men who answered American Indian to any of the race options.

^dLGA births are defined as > 90^th percentile compared with the Oken sex-and-gestational-age-specific reference population values.²²

^*P < 0.05.