DISCUSSION
Clinical decision making is an extremely complex process, given its difficulty and the consequences for the patient, which can determine their life or death. The Institute of Medicine's report on diagnosis in medicine considers that everyone will experience at least one diagnostic error in their lifetime, often with devastating consequences (31).
The uncertainty of the problem at hand (especially in the context of PC), the limited time available and the cost involved in searching for information may result in a greater use of system 1 by physicians (30), opting for intuitive and heuristic decisions, allowing quick decisions to be made. In any case, the effect of unconscious thinking on clinical decision-making is contradictory,11 the evidence on the use of heuristics in medicine is very scarce and the instruments and operational definitions for their assessment are insufficiently validated (25, 26, 32). Most of the knowledge regarding clinical decision-making and the use of intuitive strategies is based on studies conducted under experimental conditions, using simulations or vignette assessment, which are unlikely to be representative of real-life clinical encounters (29).
To deepen our understanding of the use of heuristics by general practitioners, an empirical approach has been developed that may improve our understanding of the scope of heuristics cited in routine clinical practice, and which, in contrast to previous literature "in laboratory conditions", studies PA clinical decision-making in its daily life with its organizational, temporal, and cognitive constraints.
The results suggest an extensive use of heuristics (or in any case unconscious modes of thinking) by primary care physicians: in almost half of the cases seen, the first diagnostic impression coincided with the Confirmatory Diagnosis, before any clinical intervention was made. It is known that physicians generate their diagnostic hypotheses very early, in just seconds, with very little information (27, 33) and that even this decision prior to gathering more information is associated with greater diagnostic accuracy (29, 34). The difficulty in considering this as a first impression, a heuristic of representativeness or recognition, or gut feeling stems from the lack of agreement in the scientific community on how to define these forms of unconscious thought (unknown thought). Regardless of what they are called, what they seem to demonstrate is that in many cases the decision regarding the problem that afflicts a patient is predetermined before information is gathered. Probably one of the factors that determines this is the prolonged knowledge of patients in PC (longitudinally), one of the keys to Primary Care doctors achieving a high degree of success in the management of patients' problems and protecting them from pathogenesis and overtreatment (35). In our study, most of the doctors had been treating the same list of patients for more than 10 years.
Also in our study, it was observed that in more than 80% of the cases the Confirmatory Diagnosis coincided with one of the three initial diagnostic hypotheses, which could suggest that the ease or speed with which the possible diagnosis comes to mind determines the Confirmatory Diagnosis, without being associated with statistical significance to a higher percentage of error.
The percentage of diagnostic error identified (9%) is slightly lower than that reported by Zwaan et al (37) in their study of 247 cases of dyspnoea seen in hospital (11.3%), confirming the commission of diagnostic errors identified through clinical audits. However, the percentage of these errors leading to serious patient harm is almost non-existent in our study, while in Zwaan's hospital study it was 4%, suggesting both the lower severity of cases seen in PC, the effect of longitudinally and the options for correction of previous hypotheses involved in continuous patient care over time (37). The second contribution of this research is the lack of a statistically significant association between the use of heuristics and diagnostic error. If these results are confirmed in subsequent studies, it would call into question the classical approach of authors such as Croskerry (13) who consider that the systematic use of heuristics or mental shortcuts entails a greater risk of error and validate the hypothesis of authors such as Gigerenzer and Graissmaier (38), who argue that heuristics are a useful and effective way of resolving clinical dilemmas. Some authors add that heuristics can provide a richer and broader knowledge base for making intuitive judgements and decisions (39).
The study has several limitations. Firstly, the number of participating physicians is small, but given that the methodology developed is explicit, it can be replicated in subsequent studies with larger populations, bearing in mind in any case that direct observation of clinical decision making under real conditions is complex and costly, and it will hardly be possible to design studies with large populations. Secondly, the lack of previous studies in real clinical conditions makes it difficult to compare results, but this approach provides information on what happens in real conditions, not in laboratory experiments. In this sense, this research initiates a novel approach to the study of the use of heuristics in the clinical decision process in primary care and its relationship with diagnostic error. Thirdly, there is probably a Hawthorne effect on the part of the participants in this study, as well as a certain learning bias in the knowledge that they were going to be evaluated in their attention to this type of problem (dyspnoea), and that they could improve their intervention as a result. It could also be considered as a limitation the bias that could have been produced by the evaluator's knowledge of the doctor responsible for the case evaluated, an unavoidable aspect as the structure of the electronic medical record does not allow "blind" review of the same. In any case, the percentage of errors identified (like Zwaan's study) leads us to believe that there has not been an excessively positive assessment of the cases studied. Another potential limitation of the study is that the operational definitions used to characterise the availability, representativeness and overconfidence heuristics may reflect other constructs or heuristics. However, we believe that our operational definition presents a high concordance to the conceptual framework of the heuristics selected in this case during clinical practice. It should be noted that in no case does this study aim to ascertain the ability of the participating physicians to identify cognitive biases, who, as Zwaan (27), points out, are not able to agree on when a cognitive bias is present.
The results seem to confirm the use of unconscious thinking by family physicians in the care of new episodes of dyspnoea, probably using heuristics, including representativeness, availability, and overconfidence. However, the use of these mental and intuitive shortcuts to establish a diagnosis does not seem to lead to an increase in diagnostic errors. Further research should confirm or disconfirm these results, which are in any case relevant for doctors and patients and useful for the training process of the former.