Politicians oftentimes employ different types of evidence-based appeals to legitimze their actions or substantiate their political claims. Yet, whether such evidence-based rhetoric is perceived as more credible is still unclear. Using original survey experiments, this paper explores this important question by focusing on two factors: the type of evidence and issue characteristics. First, I differentiate between "primary" and "secondary" evidence appeals. Primary evidence refers to one's own professional expertise or educational background, whereas secondary evidence refers to relying on external expert advice, research findings, or statistics. Building on "epistemic authority" framework, I expect that experiential, primary evidence appeals are more persuasive compared to external, secondary evidence. Second, I differentiate between valence and positional issues. While valence issues are characterized by a consensus on the desired outcome, positional issues include polarized preferences, increasing the chances for perceptual biases leading to the rejection of evidence. These hypotheses will be tested using original survey experiments in 5 European countries.