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Validation of a Preparation for Decision Making scale

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Abstract

Objective

The Preparation for Decision Making (PrepDM) scale was developed to evaluate decision processes relating to the preparation of patients for decision making and dialoguing with their practitioners. The objective of this study was to evaluate the scale's psychometric properties.

Methods

From July 2005 to March 2006, after viewing a decision aid prescribed during routine clinical care, patients completed a questionnaire including: demographic information, treatment intention, decisional conflict, decision aid acceptability, and the PrepDM scale.

Results

Four hundred orthopaedic patients completed the questionnaire. The PrepDM scale showed significant correlation with the informed (r = −0.21, p < 0.01) and support (r = −0.13, p = 0.01) subscales (DCS); and discriminated significantly between patients who did and did not find the decision aid helpful (p < 0.0001). Alpha coefficients for internal consistency ranged from 0.92 to 0.96. The scale is strongly unidimensional (principal components analysis) and Item Response Theory analyses demonstrated that all ten scale items function very well.

Conclusion

The psychometric properties of the PrepDM scale are very good.

Practice Implications

The scale could allow more comprehensive evaluation of interventions designed to prepare patients for shared-decision making encounters regarding complex health care decisions.

Introduction

Many screening and treatment decisions faced by patients are complex, in part because the benefit-harm ratios are unknown, they require difficult trade-offs, or the decisions depend on values that patients place on the risks and benefits. Decision aids that explain the options, clarify values, and act as adjuncts to practitioners’ counselling have been developed to assist patients with some of these complex decisions.

Trials evaluating decision aids have used a wide range of outcome measures, with varying ability to discriminate between decision support interventions, and the issue of appropriate or acceptable outcome measures has been raised [1], [2], [3], [4], [5]. In 2005, the International Patient Decision Aid Standards (IPDAS) Collaboration reached a consensus on the primary measure for evaluating patient decision aids—decision quality, defined as the extent to which a decision is informed and based on personal values [6]. There was also recognition of the importance of decision process measures which could lead to the primary endpoint, including: recognition of the need to make a decision, appreciation of one's goals and values and their importance in the decision, and reflection and discussion with one's practitioner [6].

The Preparation for Decision Making (PrepDM) scale [7] was developed to assess a patient's perception of how useful a decision aid or other decision support intervention is in preparing the respondent to communicate with their practitioner at a consultation visit and to make a health decision.

The PrepDM scale evolved over time as it was tested with different groups making health decisions. Initially the scale was used in a randomized controlled trial of a decision aid for women considering hormone replacement therapy (HRT) during and after menopause [8]. The 11-item scale, which addressed concepts of preparedness for decision making and predictors of preparedness, showed high internal consistency (α = 0.92), was significantly correlation with other validated scales [9], [10], and discriminated between the intervention and control study arms. Versions of the scale used in two subsequent studies—pre–post evaluations of decision support interventions for women considering breast cancer prevention options [11] and men deciding on treatment for early-stage prostate cancer [12], also demonstrated high internal consistency (α coefficients: 0.94 and 0.86, respectively) and consistent item total correlations.

Further revisions were made to items and wording of the scale and two new items (see Appendix: PrepDM scale item #1 and #5) were included in response to the IPDAS quality criteria [6]. Our objective was to evaluate the psychometric properties and validity of the most recent version of the PrepDM scale.

Section snippets

Participants and intervention

From July 2005 to March 2006, eligible patients at a rural academic medical center were referred by orthopaedic providers to watch a condition-specific video decision aid. Consecutive patients consenting to the study completed a pre- and post-intervention questionnaire.

Measures

The questionnaire included: (1) demographic questions; (2) the PrepDM scale; (3) the 16-item DCS; and (4) three decision aid acceptability questions. The PrepDM scale and DCS scores were calculated according to their respective

Results

From July 2005 to March 2006, 966 orthopaedic patients were referred for decision aids; 41% of the patients agreed to participate in the study by completing a take-home paper questionnaire (n = 400). PrepDM scores ranged from 1 (not useful) to 5 (very useful), with a mean (SD) of 3.7 (1.0). Demographic and PrepDM characteristics for the participants are presented in Table 1.

Discussion

The PrepDM scale was designed to asses a patient's perception of how useful a decision aid is in preparing them to communicate with their practitioner and to make a health decision. The scale demonstrates good internal consistency and reliable measurement across most levels of patient preparedness for decision making. All items showed high levels of discrimination between patients who were highly prepared for decision making and those who were not. Not surprisingly, the decision aid

Acknowledgements

Financial support for these projects were provided by the Canadian Institutes of Health Research [FRN: 42668] and the Foundation for Informed Medical Decision Making. Portions of this research were performed at Dartmouth Hitchcock Medical Center in Lebanon, NH between July 2005 and March 2006.

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