The LEADING guideline: Reporting standards for expert panel, best-estimate diagnosis, and longitudinal expert all data (LEAD) methods.

Accurate assessments of symptoms and illnesses are essential for health research and clinical practice but face many challenges. The absence of a single error-free measure is currently addressed by assessment methods involving experts reviewing several sources of information to achieve a best-estimate assessment. This assessment method is called the Expert Panel method in medicine, and the Best-Estimate Diagnosis or Longitudinal Expert All Data (LEAD) method in psychiatry and psychology. However, due to poor reporting of the assessment methods, the quality of pro-claimed best-estimate assessments is typically difficult to evaluate, and when the method is reported, the reporting quality varies substantially. To tackle this gap, we have developed a reporting guideline following a four-stage approach: 1) drafting reporting standards accompanied by empirical evidence, which were further developed with a patient organization for depression, 2) incorporating expert feedback through a two-round Delphi procedure, 3) refining the guideline based on an expert consensus meeting, and 4) testing the guideline by i) having researchers test it and ii) applying it to previously published studies. The last step also provides evidence for the need for the guideline: 10-63 % (Mean 33 %) of the standards were not reported across thirty randomly selected published studies. The result is the LEADING guideline comprising 20 reporting standards in four groups: the Longitudinal design, the Appropriate data, the Evaluation - experts, materials and procedures, and the Validity group. We hope that the LEADING guideline will assist researchers in planning, conducting, reporting, and evaluating research aiming to achieve best-estimate assessments.