This study analyzes the consequences of item nonresponse to the question about a household's total net income in the European Social Survey (2008-2018). We recognize two mechanisms in avoiding answering the income question: task complexity and question sensitivity, and apply multilevel logistic regressions to predict the probability of refusals or "Do not know" across respondents of different income levels. We find that the refusal to answer the income question is the highest for respondents with lower incomes, while the probability of selecting "Do not know" answers or refusal to answer is the same among respondents with higher incomes. The bias resulting from the correlation between response propensities and household income affects the accuracy of estimates for several attitudinal measures when income is included as an explanatory variable. We recommend reducing the risk of bias by limiting the complexity and sensitivity of the income question and accounting for nonresponse bias.