Development, reliability and validity of infectious disease specialist Nurse’s Core competence scale

Aim This study aims to develop an instrument to measure infectious disease specialist nurses’ core competence and examining the scale’s validity and reliability. Background With the increase of infectious diseases, more and more attention has been paid to infectious disease nursing care. The core competence of the infectious disease specialist nurses is directly related to the quality of nursing work. In previous researches, infectious disease specialist nurses’ core competence was measured by the tools developed for general nurses instead of specialized tools, which made it difficult to clarify the core competence of nurses in infectious diseases department. Methods Preliminary items were developed through literature review, theoretical research, qualitative interview and Delphi method. The confirmed 47 items were applied in the two rounds of data collection. Evaluation data on 516 infectious disease specialist nurses’ core competence in the first round were utilized to preliminarily evaluate and explore the scale’s constrution, while evaluation data on 497 infectious disease specialist nurses’ core competence in the second round were utilized to do reliability analysis and validity analysis. In this study, factor analysis, Cronbach’s α, Pearson correlation coefficients were all adopted. Results The final scale is composed of 34 items and 5 factors, and adopted the 5-point scoring method. The factors are Professional Development Abilities, Infection Prevention and Control Abilities, Nursing Abilities for Infectious Diseases, Professionalism and Humanistic Accomplishment, and Responsiveness to Emergency Infectious Diseases. The explanatory variance of the five factors was 75.569%. The reliability and validity of the scale is well validated. The internal consistency, split-half reliability and test-retest reliability were 0.806, 0.966 and 0.831 respectively. The scale has good structural validity and content validity. The content validity was 0.869. Discrimination analysis showed that there were significant differences in the scores of core competence and its five dimensions among infectious disease specialist nurses of different ages, working years in infectious diseases, titles, educational background, marital status and wages (all P < 0.05). Conclusions The proposed scale takes on high reliability and validity, and is suitable for assessing the infectious disease specialist nurses’ core competence. Relevance to clinical practice This scale provides a reference for clinical assessment of infectious disease nursing.


Introduction
In recent years, the global epidemic caused by infectious diseases emerged continuously [1,2]. The epidemic situation of infectious diseases such as yellow fever, Ebola hemorrhagic fever and Dengue fever is very severe around the world [3][4][5]. In particular, the COVID-19 which broke out at the end of 2019 had spread worldwide in a very short period of time, and human beings are still fighting against it until now [6,7]. The infectious diseases not only pose great threats to human health, but also cause social panic within a certain range and affect economic and political stability [8].
The World Health Organization puts forward that under current situation, the public health work is facing huge challenges. Thus, nurses are playing more and more important roles and the requirements for professional nursing care is higher and higher [9]. Cultivating professional nursing talents has already becoming an important direction for nursing development in the new era (Mueller, Burggraf, & Crogan, 2020). That's why infectious disease specialist nurses come into being. Their core competence is not only related to the quality of the infectious disease care, but also related to the effectiveness of the infectious disease treatment. It is of great significance to the protection of public health, economic development and social stability [10,11].
The core competence of the nurses refers to the sum of knowledge, skills and comprehensive qualities required in the clinical nursing care (Chan, Lockhart, Schreiber, & Kronk, 2020). Through targeted measurement and evaluation of the specialist nurse's core competence, it can be reference for their professional development, training, assessment and etc. At present, there are evaluation tools on core competence of the emergency nurses [12], operating theatre specialist nurses [13], gerontological specialist nurses [14] and general nurses [15]. But there is still a lack of quantifiable assessment tools for evaluating the infectious disease nurses' core competence. Therefore, this study compiled the Infectious Disease Specialist Nurse's Core Competence Scale, in hope that it can provide reference to the evaluation and assessment of the infectious disease specialist nurses so as to better improve the quality of the infectious disease nursing care.

Methods
This study involved three stages as illustrated in Fig. 1.

Phase 1: identification of dimensions and development of items
In the first stage, through literature review, theoretical analysis and qualitative interview, we constructed the first draft of the core competence evaluation index system of infectious disease specialist nurses which was composed of 6 primary indicators, 17 secondary indicators and 48 tertiary indicators, and adopted the 5-point scoring method. The primary indicators were Nursing Abilities for infectious diseases, Infection Prevention and Control Abilities, Responsiveness to Infectious Diseases, Professional Development Abilities, Communication and Management Abilities and Professionalism and Humanistic Accomplishment. Then, we invited experts in the field of specialized medical treatment and nurses of infectious diseases for Delphi consultation [16]. The inclusion criteria of consultation experts were as follows: (a) has engaged in clinical nursing or medical work of infectious diseases at least 15 years; (b) has intermediate level  Cronbach's α coefficient and factor analysis were adopted for item analysis. Through item analysis and exploratory factor analysis, we filtered the items and drafted a preliminary scale, which was composed of 5 factors and 36 items. And the scale was basically consistent with the index system of core competence of infectious disease specialist nurses constructed in the previous study.
Phase 3: evaluation of reliability and validity of infectious disease specialist Nurse's Core competence scale In the third stage, we conducted the second round of questionnaire survey. The core competence of 497 infectious disease specialist nurses was evaluated by 42 head nurses with the first draft of Infectious Disease Specialist Nurse's Core Competence Scale. We took a series of measures including item analysis, reliability test and validity test to filter the scale items and re-explore and verify the structure of the scale. The methods of item analysis were the same as above. Reliability analysis included test-retest reliability, internal consistency and split-half reliability. Validity analysis included content validity and structure validity. In the second round of questionnaire survey, about 10% of the subjects were randomly remarked, and the questionnaire was sent out again 2 weeks later to measure the test-retest reliability.
Finally, a scale with high reliability and validity was formed, including 5 dimensions and 34 items.

Data collection procedure and quality control
Before conducting questionnaire investigation, the research team explained the research purpose and meaning to the head nurses and organized relevant training among them. In the process of evaluation, one-on-one evaluation was adopted, namely, one head nurse just evaluated one infectious disease specialist nurse at a time. The head nurses were responsible for the evaluation of core competence on all specialist nurses in the departments. When the evaluation was over, 10% of the nurses who were tested would be randomly selected and be evaluated again by senior nurses who are experienced in management in the infectious disease department. The senior nurses were also explained with the research purpose and meaning and trained as well. The same evaluation approach was adopted again. The results showed that, the correlation coefficient of head nurse and senior nurse to the certain specialist nurse's core competence was 0.896 (P < 0.05). This demonstrated that the head nurse's evaluation on the specialist nurse's core competence was reliable, with low subjective bias. The inclusion criteria of head nurses and senior nurses: (a) have engaged in infectious disease nursing for more than 10 years; (b) have nurse in charge title or above; (c) have good communication and expression skills; (d) voluntarily participate in research. The inclusion criteria of infectious disease specialist nurses: (a) have engaged in infectious disease nursing for more than 5 years; (b) have participated in infectious disease specialist nurse training and got the certificate.
The sample size was determined by the general rule that factor analytic procedure requires a minimum of five respondents per item, but a larger sample is desirable [18,19]. In our study, ten respondents per item were required to ensure the accuracy of factor analysis. Therefore, during the two rounds of questionnaire investigations, head nurses of infectious diseases department were selected by convenient sampling method to evaluate the core competence of infectious disease specialist nurses.

Statistical analysis
Data were analyzed by SPSS 23.0 and Mplus 8.3 software.
For item analysis, items were screened with the Classical Test Theory [20] which included discrete trend method, critical ratio method, correlation coefficient method, Cronbach's α coefficient method and factor analysis method. The standard deviation of item scores represented the degree of dispersion. When SD < 0.85, it indicated that the item was not able to distinguish and was to be deleted. The total score of the scale was ranked from high to low, and the relationship between the high-score group (the first 27%) and the low-score group (the last 27%) was analyzed to judge the discrimination of the scale. It was the same to the factor loading. If the total score was less than 0.4, the item needs to be deleted. If Cronbach's α coefficient became larger after deleting the item, it indicated that the item would lower the internal consistency of the scale and should be deleted [21].
Reliability analysis referred to the consistency of the results of repeated measurement of the same object by the same method [22,23]. For reliability analysis, we used Cronbach's α coefficient, split-half reliability and test-retest reliability. Cronbach's α coefficient was used to evaluate the internal consistency reliability of the scale. The scale was divided into two parts according to the order of oddness and evenness, and the correlation between them was to calculate the split-half reliability. Two weeks later, we would conduct a test-retest on the nurses marked before, and measure the test-retest reliability.
Validity analysis referred to the analysis of the accuracy of the scale [24,25]. For validity analysis, we conducted content validity analysis and structure analysis. The validity of the content was evaluated by Delphi experts' scores which included the content validity index of the items (I-CVI) and content validity index of the scale (S-CVI). The structure analysis contained exploratory factor analysis and confirmatory factor analysis. Index value standard: The Kaiser-Meyer-Olkin (KMO) > 0.6, χ2/df < 3, Root mean square error approximation (RMSEA) < 0.08, Comparative fit index (CFI) > 0.90, Tucker-Lewis index (TLI) > 0.90, Standard root meansquare residual (SRMR) < 0.80 [26].

Ethical consideration
Research was approved by the ethics committee of Tangdu Hospital of Fourth Military Military Medical University, China (Number TDLL2019-09-13). Informed consent was obtained from all participants included in the study and they could withdraw from the study at any time for any reason. Moreover, they were assured that the questionnaires would only be used for research.

Characteristics of the participant
From January to March 2021, 540 questionnaires were distributed in the first round of survey, and 516 were effectively recovered, with an effective recovery rate of 95.56%. The average age of head nurses was (42.15 ± 5.57), and the average number of years of nursing infectious diseases was (18.75 ± 6.03). The average age of infectious disease specialist nurses was (31.02 ± 5.17), and the average number of years engaged in infectious disease nursing was (9.29 ± 4.23). From May to July 2021, the second round of questionnaire survey was conducted. A total of 517 questionnaires were distributed and 497 valid questionnaires were recovered, with an effective recovery rate of 96.13%. The average age of head nurses was (41.60 ± 4.54), and the years of nursing infectious diseases were (17.36 ± 4.76). The average age of infectious disease specialist nurses was (32.17 ± 5.77), and the number of years engaged in infectious disease nursing was (9.02 ± 3.78). Other demographic data are shown in Table 1.

Preliminary evaluation and exploration of scale Item analysis
As shown in Table 2, the results of item analysis of the 516 questionnaires in the first round showed that the item analysis values of each item were up to the standard and the items were to be reserved.

Exploratory factor analysis
EFA was used to construct the core competence structure model of infectious disease specialist nurses.
The KMO value was 0.971, the Bartley Sphericity test was statistically significant (χ 2 = 25,348.591, df = 1081, P < 0.005), indicating that 47 items of infectious disease specialist nurses' core competence scale were suitable for factor analysis.
Principal Component Analysis was used to extract factors and varimax was used to rotate factors to extract components with eigenvalues higher than 1. Then, delete the highest factor load < 0.4, factor load across two or more factors and the difference < 0.2, and the number of common factor included items< 3. According to the above criteria, items 3,7,8,10,20,23,25,26,32,36, 38 were deleted, and five common factors were extracted. The cumulative contribution of variance accounted to 72.3%.
After the exploratory factor analysis, a preliminary questionnaire of core competence of infectious disease specialist nurses was formed, including 5 factors and 36 items, which was basically consistent with the index system of core competence of infectious disease specialist nurses constructed in this study. According to the results of group discussion and professional knowledge, five factors were named, namely Professional Development Abilities, Infection Prevention and Control Abilities, Nursing Abilities for Infectious Diseases, Professionalism and Humanistic Accomplishment and Responsiveness to Infectious Diseases (as seen in Table 3).

Reevaluation of scale Item analysis
As shown in Table 2, the results of item analysis of the 497 questionnaires in the second round showed that the

Reliability analysis
As shown in Table 4, the scale and its five dimensions have ideal internal consistency and split-half reliability.
The internal consistency of each dimension ranged from 0.692 to 0.790, and the total internal consistency was 0.806. The split-half reliability of each dimension ranged from 0.764 to 0.952, and the total split-half reliability was 0.966. In addition, after two weeks, 47 infectious disease specialist nurses were randomly selected and their core competence questionnaire was scored by 3 head nurses. The test-retest reliability of each dimension ranged from 0.696 to 0.881, and the total test-retest reliability was 0.831.

Validity analysis
Content validity 30 infectious disease experts from 12 hospitals in 8 different provinces and cities in China were invited to evaluate the content validity of the scale. The results showed that the I-CVI was 0.828-0.897, and S-CVI was 0.869.

Structure validity
Exploratory factor analysis The results of principal component analysis of each dimension showed that among the factors of each dimension, only one had an eigenvalue greater than 1, the variance contribution rate ranged from 68.97 to 79.75%, and the load value of each dimension item was greater than 0.4, as shown in Table 5. 247 questionnaires were randomly selected from the 497 questionnaires, and exploratory factor analysis was conducted by principal component analysis. Bartlett Fig. 2).
The standard factor load model formed by confirmatory factor analysis was shown in Fig. 3. The factor load of each item was greater than 0.40, and all items had statistical significance (P < 0.05), indicating that the questionnaire had good structural validity.

Discrimination analysis
Discrimination analysis was conducted on the evaluation scale of core competence of infectious disease specialist nurses. T-test and analysis of variance were used to compare the core competence and scores of 5 dimensions of infectious disease specialist nurses with different demographic characteristics. The research results are shown in Table 7. The results showed that there were significant differences in the scores of core competence and its five dimensions among infectious disease specialist nurses of different ages, working years in infectious diseases, titles, educational background, marital status and wages (all P < 0.05).

Discussion
The significance and innovation of the scale Among all present researches, there was no tool targeted at evaluating the infectious disease specialist nurse's core competence. This study is of great significance to some degree since this study aims at establishing an effective system targeted at evaluating the infectious disease specialist nurse's core competence, which can provide reference to the training and assessment of the   The practicability of the scale The scale was under the guidance of Core Competence Theory [27] and designed in combination with the characteristics of the infectious diseases (Ma & Cao, 2018; Wu et al., 2020) and the actual situation of the infectious diseases [28]. In the process of constructing the scale, every dimension was endowed with a mission for infectious disease specialist nurses to fulfill. And the missions required the nurses to be able to give lectures, do scientific researches and undertake administrative work so as to advance professional development; to be able to strictly implement infection prevention and control; to be armed with solid theoretical knowledge and operational skills so as to undertake the nursing work of the infectious disease patients; to able to respect the infectious disease patients and to be able to respond to Emergency Infectious Diseases. The scale was designed for scientifically and effectively evaluating the core competence of the infectious disease nurses and providing measurement tool for carrying out clinical infectious disease nursing care and improving the specialist nurses' abilities. The higher the score of the scale the nurse got, the higher the level of the nurse's core competence was.
In this way, the scale was of practicability.
The scientificity of the scale The Infectious Disease Specialist Nurse's Core Competence Scale, featured as high reliability and validity, was finally established with 5 factors and 34 items after preliminary evaluation and exploration in the first round and re-evaluation in the second round. The cumulative explanatory variance of the five factors was 75.569%, indicating that the five factors could explain the difference in core competence of infectious diseases specialist nurses to the extent of 75.569%. The scale had a clear structure and was roughly consistent with the index system constructed in the first part, which confirmed the rationality of the design structure. Through a series of methods such as a large number of literature review, theoretical analysis, qualitative interviews, expert correspondence, etc., the comprehensive consideration of the core competence of infectious disease specialist nurses was transformed into an evaluation tool, which had a certain degree of scientificity. On the basis of reliability and validity evaluation, the differences of core competence and its dimension scores of infectious disease specialist nurses in different demographic characteristics were compared, and the influencing factors of core competence were preliminarily explored. The core competence of infectious disease specialist nurses aged 31-40 was higher than that of low and high age group; the core competence of specialist nurses who have worked in infectious disease nursing for 11-20 years were higher than those who have worked for less than 10 years and more than 20 years; the core competence of nurse in charge was higher than that of the nurse or the deputy chief nurse or above; specialist nurses with middle salary level had the highest score in core competence. The nurse in charge has longer working years and accumulated a lot of clinical experience in infectious disease nursing than younger nurse. At the same time, compared with older nurses, the nurse in charge was the core backbone of the Department and was mainly responsible for the nursing and management of infectious diseases, so the level of core competence was the highest. The core competence score of nurses with bachelor degree was higher, because they have received a higher education level and can better master clinical skills and improve clinical nursing ability [29]. Zuriguel-p é rez et al. [30] found that highly educated nurses often have better critical thinking in nursing work, which is also an important aspect of core competence. The core competence of married specialist nurses was higher than that of unmarried or divorced nurses, which may be related to the family support from relatives for nurses' work. Especially the nurses in the Department of infectious diseases are facing great work pressure and the risk of occupational exposure [31]. Family support and recognition are the driving force of their work, which can make them better put into work [32,33].

Limitations and perspectives
In this study, cross group measurement invariance analysis on the scale was not done. So it was not clear whether there were differences in the application in different groups with different characteristic [34]. And In the next step, we will analyze the invariance of cross group measurement to figure out the differences in the application in different groups. Besides, we will introduce Generalizability Theory (GT) and apply it in the re-evaluation of the scale so that we can further verify and improve the reliability and validity of the scale [35].

Conclusions
This study is the first one to develop and validate a scale for measuring the core competence of infectious disease specialist nurse. The scale in this study comprises 34 items, 11 items in "Professional Development Abilities", 9 items in "Infection Prevention and Control Abilities", 6 items in "Nursing Abilities for Infectious Diseases", 5 items in "Professionalism and Humanistic Accomplishment", and 3 items in "Responsiveness to Emergency Infectious Diseases". The scale's validity and reliability for measuring infectious disease specialist nurses' core competence were confirmed.