As life expectancy increases, the number of older people is growing inevitably, and the aging of the population has become a global trend. China has also been experiencing a rapid pace of the population aging process and has the largest older population in the world. According to China’s Seventh National Population Census in 2020, older people (≥ 60 years old) constitute around 18.70% of the total population, representing a 5.44% increase compared to the rate in 2010 [1]. The growing number of older people is a major challenge for the country's social security system and public services such as health care; meanwhile, healthy aging, proposed by the World Health Organization (WHO) as a process of maintaining functional ability to enable wellbeing in older age has gradually become a world consensus [2, 3].
Older adults typically experience a decline or loss of self-care ability due to chronic diseases, age-related frailty, etc. In addition, with the rapid process of industrialization, urbanization, and educational expansion in contemporary society, the family structure is experiencing a dramatic transition from the conventional nuclear family model to the pluralistic and decentralized family model, gradually reducing the amount of care that older people receive in their home [4–6]. A previous study based on the Chinese Longitudinal Healthy Longevity Survey (CLHLS) showed that as the population size of the Chinese oldest-old continues to expand, the demand for long-term care will increase accordingly [7]. It is foreseeable that more long-term care facilities will be generated and increasing numbers of older people, especially those who are disabled, empty nests or living alone will choose to reside in them for receiving professional care services. For older people, transitioning from their familiar homes to nursing homes is a profoundly influential life event with uncertainty and stress. Because it not only means the conversion of aging from home care to institutional care but also represents the mutual adaptation of older people to the new living environment, such as the disruption of the old social relationships and the formation of new ones [8]. In addition, several studies have reported the emergence of negative emotions such as anxiety, depression, loneliness, apprehension, and increased confusion in older people when relocating to long-term care facilities [9–11].
Nursing home adjustment can be defined as a process of overcoming discomfort, regulating negative emotional and behavioral reactions, and eventually forming a new concept of collective life and self-orientation [12, 13]. According to the transition process framework presented by Brandburg, the transition process consists of four consecutive components: initial reaction, transitional influences, adjustment, and acceptance [14]. Among them, the adjustment process is more likely to be intervened and critical in preventing adverse transitional influences associated with relocation stress. Identifying the predictors of nursing home adjustment helps to provide effective interventions, and to further promote better acceptance of older adults residing in the nursing home. As a foundation, it is imperative to develop appropriate measurement instruments. To directly assess nursing home adjustment, the nursing home adjustment scale (NHAS) was designed based on the Korean language by Lee in 2007 [15]. As one of the most used measurement instruments in this field, it has been utilized in some studies among older people residing in nursing homes in South Korea [12, 16–18]. In 2015 and 2019, the original scale was translated, validated, and finalized in both English and Chinese versions respectively [19, 20].
To date, researchers have primarily employed classic test theory (CTT) to assess the psychometric properties of the entire NHAS [15, 19, 20], which ignored the characteristics of individual responses to a single item. In contrast, as a typical representation of modern testing theory (MTT), item response theory (IRT) has been applied for reanalysis in numerous psychometric instruments in recent years [21–23]. Unlike CTT, IRT assesses the properties of each item and thus does not rely on a combination of items and allows for generalizing testing results across samples and items [24, 25]. According to IRT, a series of IRT models that can assist in determining the psychometric properties of instruments have been developed. In IRT models, there are three decisive parameters being assumed to influence the probability of achieving a specific score from the individual and the accuracy of the measurement; and correspond to the following three models: the one-parameter (1PL; ability) or Rasch model, two-parameter logistic model (2PL logistic; ability and discrimination), and the three-parameter (3PL Logistic; ability, discrimination, and guessing). In addition, the latent trait of the subject was based on the parameters of each item. Depending on the assumptions, the probabilistic relationship between response behaviors and the latent trait can also be described for each item using a monotonously increasing function, the so-called item response function (IRF) [26, 27]. Despite the advantages in certain aspects, there are still no studies to examine the psychometric properties of the NHAS based on IRT. Of note, compared to CTT, IRT also has shortcomings, for example, the limitation in the exploration of the factor structure of the entire scale [28, 29]. Therefore, a combination of the two methods can provide a more comprehensive evaluation of the psychometric properties of an instrument.
The objective of this study is to psychometrically test the Chinese version of the Nursing Home Adjustment Scale (C-NHAS) using CTT and IRT among older people living in long-term care facilities in central China, and to provide further evidence on the improvement of the applicability for the Chinese older adults.