While an empirical strategy fully dealing with the endogeneity of the “Miner”/”Partner Miner” variable is not possible with the data at hand, we test whether our results are affected when we take preferences for spending time away from the household into account. Formally, we augment the main specification reported in tables 3-6 with two regressors that capture the individual propensity to spend more time away from the family of origin. The variable “number of times away from the household” describes how many nights the male respondent was away from his household in the last year and the dummy variable “husband living elsewhere” takes value one in the females sample if the husband or the cohabiting partner is not currently living in the household. The estimated coefficients on these variables may suffer from endogeneity bias. For this reason they should not be given a causal interpretation. The purpose of including them among the controls is purely to test whether the correlation between migrant miners and HIV status is driven by a higher propensity to spend time away from the household.

# [Insert table 7]

Estimates are displayed in table 7. A first notable result is that the coefficients on “Miner”, aged 30-44, and on “Partner Miner” still positively affect the probability of HIV infection and the magnitude of the marginal effects are very similar to those estimated in table 3. These results increase the confidence that the estimated effects on HIV prevalence are actually associated with the status of being a miner or of having a miner as a partner. Similarly, in columns 5 and 6, we show that miners and women with a partner working in the mines are less likely to abstain, while they do not have any statistically significant effect on extramarital intercourses, in line with the results reported in table 4. In columns 9-14, we also investigate if our findings are robust to the inclusion of additional controls in the regression with condom usage as dependent variable. Once again, miners and women with a miner as a partner are less likely to use a condom, especially during sexual intercourse with a spouse in the women sample and with other occasional partners in the men sample.

# **6.2 Non-migrant miners: The case of Zimbabwe**

In this section, we attempt to understand whether _miners_ per se are more likely to be HIV infected or whether _migrant miners_ have a greater chance of being HIV positive, consequently playing an important role in HIV transmission. Disentangling these channels is crucial for designing appropriate prevention policies. To this end, we estimate the probability of HIV infection for miners and for women having a miner as a partner in Zimbabwe. As described in section 2, Zimbabwe has a well-developed local mining industry and the miners interviewed in the Zimbabwe DHS are therefore likely to be local miners. The same argument may be applied to women with a miner as a partner. Indeed, figures from the DHS show that the fraction of partners employed in the mining industry that lives within the household of origin is 66 percent in Zimbabwe, while the same percentage decreases to 29 percent in Swaziland and to 23 percent in Lesotho (not displayed). Furthermore, figure 2 shows that the number of migrants from Zimbabwe working in the South Africa gold mines is very close to zero.

[Insert table 8] 17