Measuring individual differences in susceptibility to decision biases has received increased attention in recent years, yet some methodological questions may hinder us from validly assessing the effects of cognitive heuristics. Surveys consisting of measures of several biases often aim to compare rate of occurrence of these biases and to compile a composite index from these measures. Unfortunately, the probability that the participant chooses the normative answer on the test questions often varies between and within studies, thus confounding the results. Another complication in the surveys used is that some incorrect answers are not necessarily the result of the studied bias. In our work, we tried to overcome these methodological challenges in a new survey of 15 cognitive biases. The results of 1127 participants provided insight into several methodological and theoretical questions about measuring individual differences in heuristic decisions.