Diagnostic Reasoning by Master Clinicians: What Distinguishes Them From Their Peers?

Introduction: Master clinicians are a group of physicians recognized in large part for their superior diagnostic reasoning abilities. However, their reasoning skills have not been rigorously and quantitatively compared to other clinicians using a validated instrument. Methods: We surveyed Internal Medicine physicians at the University of Iowa to identify the master clinicians. These master clinicians were administered the Diagnostic Thinking Inventory, along with an equivalent number of their peers in the general population of internists. Scores were tabulated for structure and thinking, as well as four previously identied elements of diagnostic reasoning (data acquisition, problem representation, hypothesis generation, and illness script search and selection). The 2-sample t-test was used to compare scores between the two groups. Results: 17 master clinicians were identied, of whom 17 (100%) completed the inventory. 19 out of 25 randomly-selected internists also completed the inventory (76%). Mean total scores were 187.2 and 175.8 for the Master Clinician (MC) and the Internist (IM) groups respectively. Thinking and structure subscores were 91.5 and 95.71 for MCs, compared to 85.5 and 90.3 for IMs (p-values: 0.0783 and 0.1199, respectively). The mean data acquisition, problem representation, hypothesis generation, and illness script selection subscores for MCs were 4.46, 4.57, 4.71, and 4.46, compared to 4.13, 4.38, 4.45, and 4.13 in the IM group (p-values: 0.2077, 0.4528, 0.095, and 0.029, respectively). Conclusions: Master Clinicians have greater prociency in searching for and selecting illness scripts compared to their peers. There were no statistically signicant differences between the other scores and subscores. These results will help to inform continuing medical education efforts to improve diagnostic reasoning.


Background
In recent years, the term "master clinician" has been used to describe physicians who have attained high levels of pro ciency in a variety of skills considered essential to clinical practice and education. Although the speci c de nition has remained elusive, master clinicians are acknowledged to be superior diagnosticians from whom trainees can learn valuable lessons. For that reason, "Master Clinician" programs have been established at sites like the University of Iowa. This study aims to distinguish elements of diagnostic reasoning that characterize master clinicians compared to peers, using the previously validated Diagnosing Thinking Inventory.

Methods
This study was approved by the Institutional Review Board at the University of Iowa. All methods were carried out in accordance with relevant guidelines and regulations, and informed consent was obtained from all participants. The investigation was split into three parts.
First, each question in the Diagnostic Thinking Inventory was classi ed into one of four categories: data acquisition, problem representation, hypothesis generation, and illness script search and selection.
De nitions for these four steps of diagnostic reasoning were adopted from Bowen and colleagues. 4 The wording of each question was scrutinized independently by two investigators (BK and MS), and results were compared. Two rounds of reconciliation were pursued in order to obtain a consensus classi cation of these questions.
Secondly, master clinicians were identi ed through a survey of all Internal Medicine physicians at the University of Iowa. Inclusion criteria were permanent faculty status, appointment within the Department of Internal Medicine, and over 50% clinical effort. Exclusion criteria were adjunct or visitor status, and research or administrative effort greater than 50%. They were asked to identify which clinicians amongst themselves are considered "master clinicians" based on their diagnostic skills. Those nominated by at least ve colleagues were designated as master clinicians. Once identi ed, they were administered the Diagnostic Thinking Inventory.
Finally, a third investigator (KF) used a random number generator to identify a sample of 25 internists not recognized as Master Clinicians who were then administered the Diagnostic Thinking Inventory.
Results were tabulated and uploaded into SAS® (SAS Institute, Cary, North Carolina). Descriptive statistics, including mean, median, and variance were calculated for the scores and subscores. The 2sample t-test was employed to compare means between the MC and IM groups.

Results
The Diagnostic Thinking Inventory was split into the above four categories, composed of 8 to 12 questions each ( Figure 1). There was agreement among the two investigators for 38 out of 41 at the rst round, and 41/41 by the second round for reconciliation.
Surveys asking for the names for master clinicians were distributed to the Internal Medicine physicians (n=82), of which 78 replied (95.1%). Seventeen master clinicians were identi ed through this process.
Master clinicians exhibited a higher total mean score (187.2), thinking subtotal (95.7), and structure subtotal (91.5) compared to the IM group, whose means were 175.8, 90.3, and 85.5, respectively ( Figure   2). The standard deviations among Master Clinicians were lower for the total (14.6) as well as thinking and structure subtotals (8.6 and 7.1), compared to IM physicians (21.8, 11.4, and 11.8, respectively). The differences in means were not statistically signi cant (0.0783 for thinking and 0.1199 for structure).
When grouped by the elements of diagnostic reasoning, the Master Clinicians still had higher scores for all four elements, although this difference was statistically signi cant for only illness script selection, where the mean MC subscore was 4.46 (0.31), vs. 4.13 (0.53) in the IM group (p-value: 0.029). For data acquisition, problem representation, and hypothesis generation, subscore means (and associated standard deviations) were 4.13 (standard deviation = 0.93), 4.38 (0.85), and 4.45 (0.46) for the IM group, compared to 4.46 (0.53), 4.57 (0.56), and 4.71 (0.47) for the Master Clinician group, respectively. The associated p-values were 0.2077, 0.4528, and 0.095, respectively (Table 1).

Discussion
This study demonstrates that the diagnostic approach of master clinicians may be different than their peers. Speci cally, master clinicians seem to be more pro cient in searching and selecting for illness scripts. Illness Scripts are de ned as "conceptual models, such as groups of diseases [or] representational memories of speci c syndromes." 4 Illness scripts are the result of experience and deliberate practice, suggesting that peer-recognized master clinicians continuously hone their understanding of key discriminating features, risk factors, and pathophysiologic mechanisms that de ne illness scripts. 5 This helps to explain ndings from previously published literature that expert diagnosticians are able to diagnose conditions using relatively few pieces of clinical data. 6 It also reinforces the observations that master clinicians improve their diagnostic skills through continuous re ection. 7,8 Interestingly, there was no statistically signi cant difference in scores among the other elements of diagnostic reasoning. Hypothesis generation and data acquisition appeared to approach signi cance but were not signi cant at the p=0.05 signi cance level. Of note, illness script selection had the lowest score in both groups, suggesting that this is a more advanced skill to master, compared to the other three.
Likewise, there was no statistically signi cant difference between the 'structure' and 'knowledge' subscores in the Diagnostic Thinking Inventory, which have been the two traditional categories used in prior analyses. Therefore, based on our analysis, it may be more appropriate to use this modi ed fourcategory breakdown to characterize the diagnostic reasoning process, using the same questions.
Strengths of our study include a robust prospective study design with high participation of staff physicians, including all of the identi ed master clinicians. The Diagnostic Thinking Instrument has been validated as a tool to identify diagnostic reasoning skills. 3 The methodology by which the investigators categorized the questions was predetermined based on established de nitions and criteria, enabling high rates of agreement after two rounds of reconciliation.
However, there are some notable limitations. The Diagnostic Thinking Inventory is a self-administered test, so it is subject to social desirability biases. Also, this study was only conducted at one institution, the University of Iowa. However, the mean scores for the master clinician group have been higher than previously reported numbers for physicians in general, suggesting that they truly possess better diagnostic reasoning skills. 8 Finally, the numbers are relatively modest (36 total), which may explain why some of the other elements of diagnostic reasoning did not demonstrate statistical signi cance. While more participants may reduce the standard deviations, it is unclear how the means would change, particularly if the Master Clinician group were expanded. Lastly, the DTI was not designed to identify what aspects of illness script search and selection are most discriminating. Regardless, our data suggest that, in these four steps of diagnostic reasoning, the ability to search and select for illness scripts is the most speci c marker of being a peer-recognized master clinician.

Conclusions
Master clinicians are recognized by peers in large part due to their diagnostic reasoning abilities. Compared to their peers in the general population of internists, master clinicians have greater pro ciency in searching for and selecting illness scripts. This aligns well with prior observations that master clinicians engage in deliberate practice to build upon their prior experiences. Replication of these ndings at other institutions may bolster such conclusions. Furthermore, these ndings inform the development of master clinician and continuing medical education programs at other institutions.  .0766