Participants
We recruited eligible clinical nurses by convenience sampling in Shenyang and Jinzhou, China, from January to March 2022. Inclusion criteria were registered nurses who have at least one year clinical work experience and gave informed consent. Exclusion criteria were clinical nurses from non-clinical departments and non-Chinese nationalities. The sample size was determined by the general guideline of factor analysis, that is, at least 10 participants responded to each item, and the 20% sample loss rate should also be considered [21]. In our study, the translated scale consists of 16 items, and at least 200 participants were needed, but a large sample is desirable [22]. According to the existing conditions, a total of 436 clinical nurses (for item analysis) and 674 clinical nurses (for psychometric evaluation) were finally recruited.
Design
A methodological study with three phases: (1) the translation and revision of the scale; (2) the exploration and evaluation of the item (n = 436); (3) the psychometric evaluation of the scale (n = 674). In addition, the samples involved in the third phase were randomly divided into two groups, one for exploratory factor analysis (EFA, n = 337) and the other for confirmatory factor analysis (CFA, n = 337). The flowchart is shown in Fig. 1.
The translation and revision of the scale
The Brislin double back-translation method was adopted to translate the ACP-SE scale [23]. First, two Chinese professors (one had experience of studying abroad, the other majored in English) translated the ACP-SE scale into Chinese, respectively. After they discussed with each other, the forward translation version was formed. Then, two foreign teachers translated the forward version into English, respectively. After they discussed with each other, the reverse translation version was formed. Finally, the reverse translation version and the original scale were compared and discussed by the above four translators and the research team to ensure the consistency of semantics and context to the greatest extent. The draft of the Chinese version of the ACP-SE scale was finally formed.
A total of seven experts were invited to revise the draft of the Chinese version of the ACP-SE scale by the Delphi expert consultation method [24]. Inclusion criteria of experts were as follows: (1) at least six years of hospice care study; (2) at least master degree; (3) at least intermediate title; (4) voluntary participants in the study. In this study, the seven expert members included three males and four females with the following credentials: working years (10.43 ± 2.99); four masters, three doctors; all held senior titles. After the cross-cultural adaptation, the draft of the Chinese version of the ACP-SE scale was used for a preliminary investigation among 30 clinical nurses to understand their opinions about the items [25]. Finally, the pre-test Chinese version of the ACP-SE scale was developed.
The exploration and evaluation of the item
We used the critical ratio method, correlation coefficient method and internal consistency for item analysis to evaluate the suitability for each item. The critical ratio was calculated by t-test for two independent samples (the first 27%, high-score group vs the last 27%, poor-score group) to determine the discrimination of the item. It is generally considered that when the critical ratio of each item ≥ 3 (P < 0.05), the item has satisfactory discrimination [26]. The item-total correlation coefficient was calculated to determine the homogeneity of the item, and the item-total correlation coefficient ≥ 0.4 indicates that the item has the appropriate homogeneity [26]. The Cronbach's α coefficient after deleting each item was calculated to determine the quality of the item. We require that the Cronbach's α coefficient of the scale would not increase if the item was deleted [26]. In addition, the preliminary EFA was completed to explore the factor loadings to assess the stability, and the recommended factor loading for each item should be above 0.40 and there was no cross loading. If the above requirements were not met, the corresponding item will be deleted [27].
The psychometric evaluation of the scale
We invited eligible seven experts to appraise the content validity of the Chinese version of the ACP-SE scale. The Likert four-point scoring system, from one point (irrelevant) to four point (very relevant), was adopted to gather responses from experts. The content validity index of the item (I-CVI) is the ratio of the number of experts giving three or four points to the total number of experts participating in this evaluation. The content validity index of the scale (S-CVI) is the average of I-CVI of all items in the scale. We require the I-CVI ≥ 0.78 and the S-CVI ≥ 0.90 [28].
EFA with principal axis factoring was completed to explore the underlying factor structure of the scale. The Bartlett’s test of sphericity was significant (P < 0.05) and the Kaiser–Meyer–Olkin (KMO) coefficient was > 0.60, indicating the suitability for EFA [29]. The requirements are as follows:(1) the factor loading of the item ≥ 0.4 and there was no cross loading, (2) each extracted common factor contains no less than three items, and (3) the cumulative explanatory variation of all common factors ≥ 40% [30, 31].
The CFA was completed to explore whether the factor model met theoretical expectations. The criteria for fitting indexes are as follows: (1) the chi-square degree of freedom (2/df) ≤ 3; (2) the root mean square error of approximation (RMSEA) ≤ 0.05; (3) the goodness-of-fit index (GFI), the adjusted goodness-of-fit index (AGFI), the tucker lewis index (TLI), the comparative fit index (CFI), and the incremental fit index (IFI) ≥ 0.9; (4) the parsimonious goodness-of-fit index (PGFI) and the parsimonious normed-of-fit index (PNFI) ≥ 0.5 [32, 33].
Also, convergent validity and discriminant validity were conducted to assess the construct validity of the scale. The average variance extracted (AVE) value and the composite reliability (CR) value were used for the convergent validity. The AVE value ≥ 0.50 and the CR value ≥ 0.70, which indicate that the scale has appropriate convergent validity [34]. The square root of the AVE value and the correlation coefficient of the factors were calculated to evaluate the discriminant validity. We require that the square root of AVE value should exceed the correlation coefficient between the corresponding factors [34].
The ACP-related attitude is closely related to ACP-SE among clinical nurses [16]. Therefore, the ACP practice preference scale for clinical nurses was adopted as a criterion instrument to appraise the criterion validity of the Chinese version of ACP-SE scale. The correlation coefficient between them was calculated as a reliable index, and the correlation coefficient ≥ 0.7, demonstrating that the Chinese version of the ACP-SE scale has optimal criterion validity [35].
The internal consistency and the test–retest reliability were performed to appraise the reliability of the Chinese version of the ACP-SE scale. In the internal consistency analysis, the Cronbach'sα coefficient and the split-half reliability coefficient were calculated to evaluate the homogeneity of the item. After two weeks, the scale was adopted to remeasure the previously labeled 80 clinical nurses, and the correlation coefficient was calculated to assess the stability of the scale across time. We require that the Cronbach’α coefficient, the split-half reliability coefficient and test–retest reliability coefficient should all be 0.7 or above [36, 37].
Instruments
The general demographic characteristics questionnaire
We developed the general demographic characteristics questionnaire after systematic literature analysis and rigorous team negotiation. The questionnaire included seven variables: age, gender, marital status, education level, working years, department, received relevant training.
The advance care planning (ACP) practice preference scale
ACP practice preference scale was previously developed by our team to evaluate ACP practice preference among clinical nurses. The scale consists of three dimensions with 24 items. The Likert five-point scoring system (very disagree to very agree) was adopted to gather responses from clinical nurses. The score ranges from 24 to 120. The higher the score is, the stronger the ACP participation preference of clinical nurses is. In our previous work, this scale was confirmed to have appropriate psychometric properties.
Data collection
After explaining the purpose and significance of the study, the researchers recruited clinical nurses with the assistance of nursing leaders in two cities, China. In phase one, seven eligible experts received the compressed package consisting of informed consent and expert consultation questionnaire via email, and were told to return within two weeks. The recovery rate of the questionnaire was satisfactory. In phase two, we invited 460 clinical nurses to participate in the survey, and 447 clinical nurses agreed to the invitation and signed the informed consent. 436 questionnaires were retained after the questionnaires with missing data were removed. In phase three, we recruited 700 clinical nurses to participate in the survey, and 682 clinical nurses agreed to participate in the study. After deleting the questionnaires with missing data, 674 questionnaires were finally retained. It takes six to eight minutes to complete the questionnaire.
Data analysis
SPSS 26.0 and AMOS 18.0 were used to complete statistical analysis. Frequency and composition ratios were adopted to describe the general demographic characteristics of clinical nurses. Item analysis was completed to evaluate the quality of the items, and the Delphi survey was adopted to assess the content validity of the scale. EFA with principal axis factoring was completed to explore the underlying factor structure of the scale. Also, the structural equation model (SEM) with maximum likelihood was completed to validate the consistency between the underlying factor structure and the theoretical expectation. The internal consistency analysis and test–retest reliability analysis were conducted to assess the homogeneity and stability of the scale.
All participants signed informed consent and filled in the questionnaire anonymously after being informed of the purpose, significance, voluntary and anonymous nature of the study. All methods and contents of this study were performed in accordance with the Declaration of Helsinki and approved by the Ethics Review Committee of the First Affiliated Hospital of China Medical University (AF-SOP-07–1. 1–01).