METHODS
Scope of the study: 4 PC centres in Granada and 6 centres in Madrid (Spain) were selected. A total of 371 cases were registered in the period 2012-2016, with 23 participating physicians, 11 of whom were women and 12 men. The mean age was 49 years (range: 29-53 years) and mean experience in PC was 22 years (range: 4-32 years).
Study design: Applying the methodology proposed in the protocol,26 a prospective study of new episodes of dyspnoea identified by the attending physician was designed. This methodology is adapted from the study protocol for patients with dyspnoea seen in Dutch hospitals developed by Zwaan et al (27). Dyspnoea was selected because it is a prevalent reason for consultation in the PC care process, there are multiple diagnostic alternatives, and it has been previously studied. The follow-up time for each patient was from the first visit for a new episode of dyspnoea to the time when the confirmatory diagnosis was made. For each patient presenting with a new episode of dyspnoea, the physician completed two questionnaires at different times (at the first visit and when the confirmatory diagnosis was made). All the patient's data and the patient's diagnostic process were recorded in the questionnaire. The existence of this parallel register was decided to avoid using the same hardware as the electronic medical record to always maintain the confidentiality of the clinical information.
Collection of information: At the time of seeing a patient with a new episode of dyspnoea, the family doctor filled in his or her first impression of the case (First Diagnostic Impression or FDI). At the end of the consultation and before seeing a new patient, he/she completed the rest of the questionnaire, which included questions about the three most probable diagnoses (differential diagnosis or DD) and the probable diagnostic judgement (JD). Finally, the physician was asked to estimate his or her confidence in having made the correct diagnosis in terms of probability from 0 to 100%. Depending on the clinical picture, each doctor could request further diagnostic tests after the first visit or conduct new clinical encounters, which were recorded in the electronic medical record. Once the episode of dyspnoea had ended, a second questionnaire was filled in again, including the confirmatory diagnosis (CD) and the time elapsed from onset to diagnosis, information filled in by the family doctor himself.
Clinical audit process: A structured search of the literature was carried out to obtain clinical practice guidelines on the care of dyspnoea in PC; as no such guidelines were available, a guide was drawn up based on the existing literature, which was agreed with the participating doctors. Based on this, an evaluation questionnaire was drawn up and completed by the evaluators after reviewing the electronic medical records.
Each of the cases was evaluated by two evaluators, Primary Care physicians, participants in the study, with extensive accreditations in clinical care. If there were differences between the assessment of the two assessors, the case was reviewed by a third assessor. The latter were authorized to access it as they were also participants in the project but belonged to different centres.
They reviewed each of the episodes and completed the questionnaires which included information on their personal assessment of whether the appropriate tests had been ordered, whether the diagnostic process was correct, and whether the diagnosis was correct, following the methodology developed by Zwaan et al (27).
Operational definition of the heuristics: For the operational approach to the use of the Representativeness and Availability heuristics, the previously published study protocol was used, which analyses the cognitive aspects of the diagnostic process of dyspnoea by primary care physicians (26), the definition of which is described below:
Representativeness: the possible use of the representativeness heuristic is considered when the Confirmatory Diagnosis of dyspnoea coincides with the First Diagnostic Impression made by the physician when identifying a new episode of dyspnoea, before initiating any clinical intervention (anamnesis, physical examination, or request for diagnostic tests. It would form part of what has been called "gut feeling "(28) or "first diagnostic impression "(29), identifying the degree of similarity of the sample (the new case) with the population (the set of cases of that diagnosis).
Availability: the availability heuristic is considered likely to be used when the confirmatory diagnosis falls within the three diagnostic hypotheses included in the Differential Diagnosis, made after the anamnesis and physical examination and before making the diagnostic judgement. It would identify the diagnostic options that are most quickly retrieved from memory (30).
Overconfidence: The presence of "Overconfidence" in the diagnosis was estimated if the confidence in the diagnosis was higher than average in the study subjects (75% on a scale from 0 to 100%) (Fig. 1).
Operational definition of Diagnostic Error: In the clinical audit the assessors assessed whether the general practitioner ordered the appropriate tests, whether these were correctly interpreted, whether the diagnostic process was correct and whether the final diagnosis was correct. In cases where the confirmatory diagnosis was not assessed as correct by the assessors, a diagnostic error was considered to have occurred.
Statistical analysis: Statistical analysis of the data collected was performed using the R statistical package. The frequency of the use of heuristics, the concordance between diagnoses in their different phases, First Diagnostic Impression, Differential Diagnosis, Diagnostic Judgement and Confirmatory Diagnosis, as well as the frequency of diagnostic errors were estimated. A bi-variate analysis was performed to analyse the relationship between the use of each of the 3 heuristics and the diagnostic error or success. Associations are expressed as OR with their 95% confidence interval, together with the Chi-square and Fisher tests.