Medical judgements require doctor’s belief based on the solid scientific evidence provided by empiric inductive experience. Yet, it is not infrequent that scientific data are unavailable, unreliable or controversial, such that the empirical evidence is not solid enough to allow doctors to build their own belief and make a final choice. Here we ask whether it is feasible to achieve a real and justified belief in medical affairs when scientific data are missing. We suggest a novel procedure to reach a quantifiable degree of belief which ultimately leads to medical judgement. To describe the state of medical affair under examination, we draw a sentence in the logical form "if x, then y" with just two possible answers: yes or no. Then, we examine five sources leading to doctor’s belief, namely 1) Evidence-Based Medicine levels, 2) individual experience, 3) collective knowledge, 4) logical reasoning and 5) confounding factors like chance, emotivity, cognitive bias. Every one of the five factors contributing to formulate a medical judgement is supplied with a given value of belief, so that negative values stand for negative answers and vice versa. A single number is accomplished, such that a total value of belief below zero is counted as negative, above zero as positive. In conclusion, we provide a quantitative approach to cope with the frequent medical cases where qualitative factors like emotional issues, personal beliefs, wisdom of the crowds, confirmation bias, narrative fallacy are more influential than scientific evidence in driving doctors to gain belief and formulate judgements.