Individual records, referred to personal interviews of a survey on income carried out in Modena during 2012 and tax year 2011, had been matched with their corresponding records in the Ministry of Finance databases containing the fiscal incomes of tax year 2011. The analysis of the resulting data set suggested that the fiscal income was generally more reliable than surveyed income, but in the literature the exact opposite is often assumed. Moreover, the obtained data set enables identification of the factors determining over- and under-reporting, as well as measurement error, through a comparison of the surveyed income with the fiscal income, only for suitable categories of interviewees: the taxpayers who are obliged to respect the law (the constrained sector), and taxpayers who have many possibilities to evade (the unconstrained sector). The percentage of under-reporters (67.3%) was higher than those of over-reporters (32.7%). Level of income, age, and education were the main regressors affecting the measurement errors and the behaviours of taxpayers. Estimations of tax evasion and the impacts of personal factors affecting it were carried out following different approaches. The average of individual propensity to tax evasion was 25.93% of the corresponding fiscal income. The potential total tax evaders were about 10%
