According to the World Alzheimer Report , approximately 46.8 million individuals are living with dementia globally. The number has not plateaued and it is predicted that it will increase to 131.5 million individuals by the year 2050 . Therefore, large demands on caring for older people, especially those with dementia, are needed and such burden is usually relied on informal caregivers. Informal caregivers have been viewed as invisible second patients . Indeed, providing care to a family member with disease can cause emotional, physical, and financial burden to the informal caregivers [4,5,6]. Among caregivers taking care of family member with different types of disease, those taking care of people with dementia (PWD) appear to have greater levels of psychological burden. Some research has reported that caregivers of patients with Alzheimer’s disease (AD) have a higher prevalence of depression and anxiety than caring for patients with other illnesses [6,7,8]. A meta-analysis comprising 17 studies (N = 10,825 participants) reported a high prevalence of depression (34.0%) and anxiety (43.6%) for caregivers of patients with AD . In Taiwan (where the present study was carried out), similar prevalence rates have been reported: 23.7–43.8% at risk of depression and 37.4% at risk of anxiety among informal caregivers of PWD [10, 11]. Therefore, the mental health of caregivers who take care of PWD should also be taken care of by healthcare providers.
The model proposed by Pearlin et al.  provides a potential psychological framework for healthcare providers to tackle mental health of caregivers of PWD. More specifically, the Stress Process Model (SPM) comprises the caregiving context (e.g., social and economic characteristics). Also, during the process, stressors (including objective indicators such as problematic behavior and subjective indicators such as burnout felt by caregivers) lead to psychological manifestations (e.g., depression, anxiety) via some mediators such as coping strategies . Therefore, behavioral disturbances, particularly angry or aggressive behaviors among PWD, are objective stressors associated with caregiver depression [13,14,15]. Similarly, caring for PWD increases caregiving burden, a type of subjective stressor, and such subjective burden also increases the risk of having depression and anxiety symptoms . In sum, behavioral and psychological symptoms of dementia (e.g., irritability, agitation, aggression, apathy) together with the caregivers’ caregiving burden are potential stressors that can result in impaired mental health among caregivers of PWD [15, 17].
The burden experienced by caregivers is a result of many factors. As individuals gradually lose the ability to care for themselves, there is increasing need for supervision and assistance. Novak et al.  have identified five dimensions of subjective burden comprising (i) time-dependence burden (i.e., time cost of the caregiver), (ii) developmental burden (i.e., the caregivers’ feelings of being ‘off-time’ in their development with respect to their peers [e.g., missing out on what others do because of their caring duties]), (iii) physical burden (i.e., caregivers’ feelings of chronic fatigue and damage to their physical health, (iv) social burden (i.e., caregivers’ feelings of role conflict), and (v) emotional burden (i.e., caregivers’ negative feelings toward their care receivers). The five dimensions of subjective burden may result from the individual’s unpredictable and often bizarre behavior [18, 19]. Studies of caregiver burden have also shown that increases in the care-receiver’s behavioral and psychological symptoms are strongly correlated with caregiver burden [15, 20,21,22]. Moreover, care-receiver’s behavioral and psychological symptoms (e.g., hallucinations, irritability, depression) are significant predictors of caregiver burden .
One study by Werner et al. assessed four dimensions of affiliate stigma—interpersonal interaction, concealment, structural discrimination, and access to social roles conducted . Caregivers of people with Alzheimer’s disease have especially high levels of affiliate stigma in the four aforementioned dimensions. Such affiliate stigma prevents informal caregivers from seeking the services that might reduce caregiver burden. Other family members may blame informal caregivers for providing a poor home environment or mismanaging PWD . Informal caregivers may lose their jobs due to managing symptoms of PWD in emergency situations related to their wandering, falls, and basic needs. These may include employment discrimination or other forms of structural discrimination as well as loss of social relationships and experiences of harsh social judgments . Therefore, caregivers may internalize negative stereotypes from the social stigma, resulting in affiliate stigma. In brief, affiliate stigma is a type of internalized stigma (i.e., the caregivers internalize the stigma themselves because of their relationship with PWD), and the negative effects of internalized stigma on mental health of stigmatized populations have been widely reported [26,27,28].
From the information mentioned above, affiliate stigma is another important factor that could contribute to caregiving burden and psychological distress of caregivers of PWD. Many caregivers suffer from stigma experiences because of their family member’s mental illness (i.e., courtesy stigma as defined by Goffman ), and such stigma experiences may be internalized by the caregivers and become affiliate stigma . In other words, when a society treats the caregivers of PWD with negative perceptions, attitudes, emotions, and avoidant behaviors, caregivers are at risk of having negative experiences in emotional (e.g., anxiety), social (e.g., family burden) and interpersonal (e.g., isolation) aspects . Indeed, empirical evidence has shown strong associations between affiliate stigma among informal caregivers and negative outcomes, including caregiver burden [11, 31], quality of life , depression [27, 28], anxiety [27, 28, 31].
In order to provide high quality programs to improve the mental health of caregivers who take care of PWD, it is crucial for healthcare providers to better understand the psychological mechanisms that underpin their psychological distress such as depression and anxiety. More specifically, different factors (e.g., PWD’s clinical characteristics and caregivers’ demographics) should be tested to yield the most important factors for healthcare providers to foster an efficient program. The best way to investigate the psychological mechanisms is to use a well-established theory or model. Therefore, the present study was guided by the SPM and proposes two mediation models (a parallel mediation model and a sequential mediation model). More specifically, the present study proposed and tested the mediating role of affiliate stigma and caregiver burden after controlling for several confounding variables associated with the PWD’s behavioral and psychological symptoms (e.g., PWD’s age, sex, marital status, employment status, education and relationship of caregiver, and patient’s age, sex, marital status). The present study’s simplified SPM retains the following factors derived from the original SPM: background information (treated as the confounding variables); primary stressors, including behavioral and psychological symptoms (treated as the independent variables), affiliate stigma, and caregiver burden (treated as the mediator); and depression and anxiety (treated as the outcome). While the PWD’s conditions cannot be changed, reducing affiliate stigma or caregiver burden could be effective in improving caregiver mental health if either of them was found to be a significant mediator. Furthermore, by separating stressors into affiliate stigma and caregiver burden, the present study also addresses the question of which approach caregiver support services should be more emphasized.
To the best of the present authors’ knowledge, no empirical evidence has been reported regarding whether the SPM could be an effective model in explaining mental health consequences among caregivers of PWD. Therefore, the present study sought to address this knowledge gap in the literature on PWD through two types of mediation model examining the severity of neuropsychiatric symptoms that affect caregiver depression and anxiety. It was hypothesized that caregivers experiencing increasing levels of affiliate stigma would be more likely to report higher levels of depression and anxiety, and that the relationship between neuropsychiatric symptoms and caregiver mental health would be mediated by caregiver burden and affiliate stigma.