Validating patient and physician versions of the shared decision making questionnaire in oncology setting

Introduction

Cancer is one of the most important causes of death and human health issues during the past decades.¹ According to the World Health Organization (WHO) report, cancer accounted for near 9.6 million deaths in 2018 globally.² The most common cancer types include lung, breast, prostate, and gastrointestinal tract cancers. With the development of advanced diagnostic tools and the progress made in various cancer treatments, the survival rates of cancer patients have kept increasing. In addition to the medical parts, efforts have been made to improve the quality of their physical and psychosocial support during the past few years.¹ However, many of the cancer survivors still experience several unmet needs, including education, information, communication and provider relationship.³

In order to achieve the quality of cancer care, healthcare providers should have good communication with cancer survivors. Indeed, it is claimed that the optimal decision for a patient can be made using the model of shared decision making; that is, at least a clinician and a patient share information to each other. Clinicians offer treatment options with potential risks and benefits; patients express preferences and values.⁴ Through shared decision making, active participation in the decision-making process is increased with the following benefits: improved knowledge for patient, decreased decision conflict between clinicians and patients, and facilitated decision reaching.⁵ Additionally, less anxiety and better treatment outcomes have been proposed to those patients who used shared decision making.⁶ The benefits of shared decision making are also been proposed for cancer survivors that oncological decisions made by shared decision making can enrich the treatment process for patients to gain benefits from curative cancer treatments.⁷

Thus, the 9-item Shared Decision Making Questionnaire (SDM-Q-9) and the Shared Decision Making Questionnaire-physician version (SDM-Q-Doc) have been developed recently.^8-10 Both measures were found to be feasible and effective in interventions.¹¹ However, psychometric properties of both SDM-Q-9 and SDM-Q-Doc need additional investigation because of the following reasons. Specifically, to the best of our knowledge, only two studies have validated the SDM-Q-9 using a sample of breast cancer patients or a sample majority consisted of colon, breast, and stomach cancer patients.^12,13 Another study has validated the SDM-Q-Doc using a sample of medical oncologists who rated SDM-Q-Doc for their oncology patients with majority diagnoses were colon cancer (40.4%) and breast cancer (35.2%).⁷ Thus, psychometric evidence of SDM-Q-9 and SDM-Q-Doc is understudied in the oncology setting. For example, we are unsure whether SDM-Q-9 is sound and valid for cancer survivors other than the aforementioned cancers; we have no information whether SDM-Q-Doc is reliable and can be applied to cancer survivors when the physician raters are not oncologists. Given that the scientific nature is to accumulate evidence using different methods,¹⁴ especially that the psychometric properties are highly depended on the studied samples,¹⁵ further psychometric evaluation for SDM-Q-9 and SDM-Q-Doc is thus crucial. Specifically, SDM-Q-9 should be tested among different types of cancer diagnoses and SDM-Q-Doc should be examined among various areas of physician expertise.

In addition, to our knowledge, both SDM-Q-9 and SDM-Q-Doc have not been investigated for their measurement invariance and differential item functioning (DIF) across sex. Given that males and females usually have different thoughts and diverse interpretations in item descriptions,¹⁶ it is essential for healthcare professionals to understand whether male and female cancer survivors interpret the SDM-Q-9 items similarly; whether male and female physicians interpret the SDM-Q-Doc items similarly. After ensuring that the measures are measurement invariant and have no DIF items across sex, healthcare professionals can conclude that males and females report the same thing in their shared decision making using SDM-Q-9 and SDM-Q-Doc. In other words, we need not to worry about the gender bias when using either SDM-Q-9 or SDM-Q-Doc.

The purpose of this study was to investigate the psychometric properties of SDM-Q-9 and SDM-Q-Doc using comprehensive and thorough psychometric methods in an oncology setting.

Materials and Methods

Results

Discussion

This study, to the best of our knowledge, is the first to examine the measurement invariance and DIF across sex for both SDM-Q-9 and SDM-Q-Doc in different diagnoses of cancer survivors, including gastrointestinal cancer, breast cancer, multiple myeloma, skin cancer, lung cancer, and genitourinary cancer. In addition, comprehensive and thorough evidence in their psychometric properties was examined. Specifically, the unidimensionality was verified by our findings from CFA and Rasch models for both SDM-Q-9 and SDM-Q-Doc. Our DIF and measurement invariance findings further suggested that male cancer survivors did not have different interpretation in the SDM-Q-9 items from female cancer survivors; the male physicians did not interpret the SDM-Q-Doc items differently from female physicians. Moreover, both SDM-Q-9 and SDM-Q-Doc were moderately correlated to relevant external criteria listed in our Table 5. Therefore, we tentatively concluded that both SDM-Q-9 and SDM-Q-Doc can be feasibly used for healthcare professionals to assess the degree of shared decision making among different types of cancer survivors.

As we compared our findings to previous studies on cancer survivors,^7,12,13 slightly differences were found. Wu et al¹² found that item 1 in the SDM-Q-9 was misfit for the breast cancer survivors, and they recommended removing this item from SDM-Q-9. In contrast, our findings indicate that item 1 fit in the SDM-Q-9; however, item 1 as compared with other items did perform worse in the unidimensionality. Specifically, both infit and outfit MnSq of item 1 were the highest among the MnSq of other items. That is, item 1 was deviated from the underlying concept of shared decision making in the SDM-Q-9; however, the deviation is strong and unacceptable in the findings from Wu et al¹² but is weak and acceptable in our findings. Additionally, Calderon et al¹³ like Wu et al¹² found that item 1 may jeopardize the unidimensional structure in the SDM-Q-9. Calderon et al¹³ found that the SDM-Q-9 could have one-factor structure if removing item 1; contrarily, the SDM-Q-9 fit better to a two-factor structure if item 1 retained in the questionnaire. A possible reason is the different samples: we recruited a sample with more heterogeneous diagnoses in cancers than did Wu et al¹² and Calderon et al¹³ Given that our sample was more diverse than the samples of Wu et al¹² and Calderon et al,¹³ we would recommend retaining item 1 in the SDM-Q-9. Nevertheless, the psychometric evidence of SDM-Q-9 is still insufficient, and future studies are warranted to examine whether item 1 should be retained.

Calderon et al⁷ recently studied the psychometric properties of the SDM-Q-Doc, and they found that the SDM-Q-Doc was significantly correlated to physician satisfactory. Our findings also demonstrated similar correlation between SDM-Q-Doc and physician satisfactory. However, the factorial structure of SDM-Q-Doc was found to be different between the findings of Calderon et al⁷ and those of ours. Specifically, Calderon et al⁷ used exploratory factor analysis and CFA to conclude a two-factor structure for the SDM-Q-Doc. In contrast, we used CFA and Rasch model to conclude a single-factor structure for the SDM-Q-Doc. We suspected that the number of recruited physicians could be a reason to cause such a difference. Calderon et al⁷ recruited 32 oncologists and we recruited a total of 154 physicians across three fields of expertise (gynecologist, oncologist, and urologist). Although the 32 oncologists in the study of Calderon et al⁷ rated the SDM-Q-Doc on 520 cancer survivors with different diagnoses, we can say that the two-factor structure of SDM-Q-Doc was solely based on the perspective of the 32 oncologists. On the other hand, the number of physicians in our study was much larger than that of Calderon et al⁷ Thus, the representativeness of our participants should be stronger than that of the participants in Calderon et al⁷ However, future studies are warranted to confirm the factorial structure of SDM-Q-Doc because to the best our knowledge, only Calderon et al⁷ and we have examined the factorial structure for SDM-Q-Doc on cancer patients.

In addition to the three studies on cancer patients,^7,12,13 our psychometric results were in line with the studies on populations other than cancer patients. In the SDM-Q-9, Scholl et al³³ found that it has high internal consistency (α = 0.92) with satisfactory corrected item-total correlations (0.52 to 0.85) among patients with type 2 diabetes, chronic pain, and depression. De las Cuevas et al,³⁴ also found satisfactory internal consistency (α = 0.89) in the SDM-Q-9; they further concluded that the SDM-Q-9 has a unidimensional structure after removing item. In the SDM-Q-Doc, Simon et al³⁵ like our results demonstrate the unidimensional structure derived from Rasch analysis.

Conclusion

This study validated the SDM-Q-9 for use among various types of cancer survivors and the SDM-Q-Doc for use among physicians with different areas of expertise on their cancer patients. Given the increasing number of cancer survivors and the importance of shared decision making in oncology setting, using both measures to evaluate the level of shared decision making can help healthcare professionals provide personalized care efficiently ana subsequently improved the treatment outcomes.

Ethical approval

All procedures performed in the study involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. The study was approved by the Research Ethical Committee of Qazvin University of Medical Sciences, Qazvin, Iran. Written informed consent was obtained from all subjects. Informed consent was obtained from all individual participants included in the study.

Competing interests

The authors declare no conflicts of interest, both financial and non-financial, for this study.

Funding

No fund was received to conduct this study.

Authors’ contributions

BN and AHP collected the initial data. CYL, BN, CCL and AHP were involved in the conception of the study, performed the analyses, and drafted the manuscript. AB, VI, and MB were involved in the interpretation of the results from the analyses.

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