younger, the coefficient on one of the informal pooling variables - monthly expenditure on children's education (LEDKIDS) - becomes negative and significant to the probability of contribution. Since contributions up to the MPG threshold may be motivated by a preference for pooling, this may be evidence of younger workers substituting the pooling component of the formal pension system with informal pooling. In the second probit (PROBIT 2), I separate the Chilean system's pooling element from its saving element by interacting each regressor with the dummy variable MPG (the binary variable equal to 1 if the respondent had contributed to the system for at least 240 months), to capture the different set of incentives that obtain once affiliates become eligible for the pooled annuity guaranteed by the government. The only interacted variable that was not dropped during a general to specific procedure was the interaction of MPG with the log of imputed household rent (LRENT). Including the interacted variable influences the significance of other variables in the model. The estimated coefficient on firm size (FSIZE) in the regression on the male sample that was negative and significant (10% level) in the first probit, is no longer significant. The coefficient on (log of) monthly expenditure on children's education (LEDKIDS) that was not significant on the full sample of men in the first probit, significantly (10% level) lowers the likelihood men are contributing to the pension system in the second.

In the regressions on the sample of women, including the interacted term also changes the results. Female heads of household are significantly (10% level) more likely to contribute in the second specification. However, women in rural areas and those working in the agriculture industry are significantly (both at 10% level) less likely to contribute. Like men, women who cross the eligibility threshold for the minimum pension guarantee are 46% less likely to continue contributing to the pension system.

The estimated coefficients on the interactions of MPG and LRENT in the model for men and women are very revealing. For men, the likelihood of making additional contributions beyond the minimum required for the guaranteed annuity, is significantly (1% level) lower the greater the rental value of their home. Since contributions to the system beyond 240 months are mainly a form of saving, men who cross the threshold and become eligible for the pooled benefit may prefer to substitute saving in the pension system with saving outside the system in the form of housing. The negative coefficient on the interacted variable becomes statistically significant for samples of working men aged 49 and older. The opposite is true for women, although the result is less significant (10% level). The greater the rental value of the homes of women who have crossed the contribution threshold for the minimum benefit, the more likely they are to make additional contributions. Since the coefficient on MPG in the same regression is negative and significant (10% level), it is likely that the coefficient on the interacted term is capturing the positive effect of income.

Even after controlling for "access" (industry of employment) found to be significant in Packard, et al (2001), the variables capturing "demand" (expectations, alternative investments, and portfolio choices) have a significant impact on whether workers contribute. In fact, including the wider range of "demand" variables constructed from the PRIESO data leaves most of the "access" variables that were significant in the contribution probits in Packard, et al (2001), statistically insignificant. This said, full26