Cross-Country Regressions of Average STI Prevalence on Per Capita Income and the Gini Coefficient of Inequality for Low- and High-Risk Groups, Selected Countries| Category | Average prevalence of STIs in low-risk groups | Average prevalence of STIs in high-risk groups |
| Gross national income purchasing power parity per capita, log, 19~2001 | -0.862** | -0.194+ |
| Gini index, 1990s | 7.731** | 2.73* |
| Dummy for syphilis | 0.093 | -0.051 |
| Dummy for chlamydia | 1.992** | 0.308 |
| Dummy for herpes | 3.611** | 1.507** |
| Constant | -0.515 | -1.751 |
| R2 | 0.45 | 0.16 |
| Number of countries | 204 | 147 |
Source: Authors' calculations from Schmid and others 2004.
Note: * = probability of less than 0.05 percent; ** = probability of less than 0.01 percent. Positive numbers indicate a probability of 0.1 to 0.2 percent. Both regressions pool data across these STIs: syphilis, chlamydia, and herpes. The coefficients of the dummies show that the estimated prevalence rates are significantly higher for herpes than for the other diseases. Among low-risk groups, the prevalence of chlamydia is higher than that of syphilis. Standard errors (not shown) are estimated using the White correction for heteroskedasticity under the assumption that the observations for a single country are comparable to a cluster of data. Other explanatory variables that were unsuccessful in explaining a significant proportion of the variance included percentage of the population foreign born, percentage of the population that is Muslim, male-to-female literacy gap, urban male-to-female population ratio, and military personnel per 1,000 urban population.