Validation d'une échelle de mesure : exemple de l'échelle française d'évitabilité des effets indésirables médicamenteux

Validation of a Measurement Scale: Example of a French Adverse Drug Reactions Preventability Scale

¹ Service de Pharmacologie Clinique, Centre Midi-Pyrénées de Pharmacovigilance, de Pharmacoépidémiologie et d'Informations sur le Médicament ; Inserm U657, Faculté de Médecine, Toulouse, France
² Service de Pharmacologie, Centre Régional de Pharmacovigilance, Hôpital Claude Huriez, CHRU, Lille, France
³ Département de Pharmacologie, Université Victor Segalen, CHU Pellegrin-Carrère, Bordeaux, France
⁴ Centre Régional de Pharmacovigilance Alsace, Hôpitaux Universitaires de Strasbourg, Strasbourg, France
⁵ Centre Régional de Pharmacovigilance et d'Informations sur le Médicament, Service de Pharmacologie, CHRU, Tours, France
⁶ Centre Régional de Pharmacovigilance, Hôpital Fernand Widal, Paris, France
⁷ Centre Régional de Pharmacovigilance de Bourgogne, Hôpital Général, Dijon, France
⁸ Centre Régional de Pharmacovigilance, Hôpital Edouard Herriot, Lyon, France

Reçu : 9 Février 2004
Accepté : 16 Mars 2004

Résumé

La plupart des études sur les effets indésirables médicamenteux (EIM) montrent qu'un certain nombre sont "évitables". Des méthodes de mesure de l'évitabilité des EIM existent mais aucun auteur n'a clairement évalué la validité de telles méthodes. Ainsi, à ce jour, aucune échelle de mesure de l'évitabilité ne représente un "gold standard". Pour être validée, une échelle doit posséder les qualités d'un bon instrument de mesure : la convenance (ou validité de contenu), la fiabilité, la validité contre critère et l'applicabilité. Ce travail présente les deux premières étapes d'une étude de validation d'une échelle française d'évitabilité des EIM (convenance et fiabilité). La première étape a consisté à construire une échelle d'évitabilité (choix et formulation des items, choix d'un score global et de catégories d'évitabilité, par consensus entre experts). Durant la seconde étape, plusieurs experts ont testé cette nouvelle échelle pour évaluer l'évitabilité d'un échantillon d'EIM. La compréhension de certains items et l'accord interjuges se sont révélés médiocres. Cette étude montre la faisabilité d'une étude de validation et surtout la nécessité de poursuivre cette démarche afin de disposer d'une échelle de mesure fiable d'évaluation de l'évitabilité des EIM.

Abstract

Adverse drug reactions (ADRs) have been recognised as an important cause of hospital admission. Most of these drug-related admissions were expected ADRs and, thus, partly preventable. However, as far as we know, the assessment of the preventability of ADRs was addressed in only two studies performed in France. In contrast, several other studies have been performed, mainly in the USA, and using different methods of assessing preventability. None of these methods were clearly evaluated with regard to reproducibility, validity or relevance. The purpose of this study was to initiate the validation of a French preventability scale. Here, we propose the first two phases of validation: the content validity and reliability of the scale. A working group of pharmacovigilance experts has been specifically established for this purpose. The content validity was assessed by collecting items representative of preventability. The choice and the formulation of items and a proposal of a score (global and for each item) were adopted after the consensus of the experts. A definitive version of the ADR preventability scale was used for the assessment of reliability. During the second phase, experts independently tested the new scale from observations of ADRs (49 central nervous system haemorrhages with antivitamine K). The concordance of the experts' judgements was calculated using two statistical methods (Kappa statistic and correlation coefficient). The content validity phase was performed during several workshops where experts discussed the choice and formulation of the best items. We decided to construct a scale with a small number of items, allowing a rapid evaluation of the preventability of ADRs. On the basis of a global score, four categories of preventability of ADRs ("preventable", "potentially preventable", "unclassable", "not preventable" ADRs) were proposed. The agreement of experts regarding the global score was low, with a poor correlation coefficient value (coefficient interclass = 0.491). Classification of ADRs in the four categories by the experts showed discrepancies (Kappa = 0.1136).The preventability assessment using this scale was feasible, although poor concordance between the judges has raised some questions. Several experts found use of this scale difficult in terms of a clear understanding of the items, and found that two of them were redundant. We have oversimplified some items and revision of their formulation will be necessary. Moreover, most of ADR notifications were poorly documented, resulting in a frequent choice of an "unevaluable" item. This represented an important bias in the calculation of the global score. This experience suggests the need for further studies to improve this French ADR preventability scale and validate it in differing circumstances, in order to provide a useful tool to enhance the rational use of drugs.