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We first examine whether potential differences in WTP for groundwater quality and quantity attributes pre- and post-protest Z-DQMD-FMK due to systematic differences in the observable characteristics of the samples. In Table 2 we report the sociodemographic characteristics for the full sample and the two subsamples, and test for mean equality of age, income, share of male respondents, share of respondents with tertiary education, and share of respondents in full employment. Mean age and mean annual household income for the full sample are 44 years and HRK119,052 (€16,081) respectively. Approximately 28% of the respondents have completed tertiary education while 59.7% are in full time employment. Column 4 reports the test results. The pre-protest and post-protest samples are equivalent with respect to these observable socioeconomic characteristics. In addition, the protest response rate did not appear significantly different before and during the period of instability. The equivalence of the two subsamples suggests that there was no self-selection at least with respect to the observable characteristics.