Participants
Participants in this study comprised 162 children with CP receiving rehabilitation treatment at a hospital or community welfare center or attending a school for physical disabilities, and their mothers. Sampling was done across the country, except Jeju Island. The criteria for selection of participants were 1) children with a medical CP diagnosis 2) mothers of children ranging from 3 to 18 years old 3) mothers who responded three times during the two-year study period. The study was approved by the Research Ethics Board of the Jeonju University on 14 November 2013(ethical approval code number: Jeonju University IRB-1041042-2013-1). The mean age of children with CP was 9.6 years (SD = 4.69). The general characteristics of participants are shown in Table 1.
Measure
Gross Motor Function Classification System (GMFCS)
GMFCS was used to evaluate the gross motor function of children with CP. Children's motor skills are assessed on a basis of five levels, with level 1 being able to walk without any restrictions, level 2 being able to walk with restrictions, and level 3 being able to walk without trunk support using canes, crutches, or walkers. Level 4 indicates that a child’s walking is limited but they are able to move independently using an electric wheelchair or other means of transportation, and level 5 indicates that mobility is severely limited even with assistive devices (24). Park (25) reported that the coefficients ranged from 0.690 to 0.789 and the GMFCS remained stable in children with CP aged 2 to 12 years.
Parenting Stress Index
The Korean Parent Stress Index Short Form (K PSI-SF) was used to evaluate the mothers’ parenting stress. The K PSI-SF is a tool for the identification and diagnosis of parenting-related stress, and it is designed to measure the relative stress level in a parent-child relationship. It can be used by parents of children over one month old. It consists of three domains including parent distress, parent-child dysfunctional interaction, and difficult child characteristics. The validity and reliability of K-PSI-SF was confirmed through Rasch analysis, and the internal consistency of the entire test was reported to be .92 (26).
Procedure
To investigate changes in the parenting stress of mothers raising children with CP, 162 children according to the selection criteria were sampled and data were collected in the first year. This study was approved by the Jeonju University Research Ethics Committee (Jeonju University IRB-1041042-2013-1). In Wave 1, data on the GMFCS level and parenting stress were investigated, and in Wave 2 and 3, only data on parenting stress were investigated. The level of GMFCS was evaluated by a physical therapist who had treated the child for more than six months. Participants in Wave 1 also participated in Wave 2 and 3. The mothers responded to the K-PSI-SF. After the third evaluation, it was investigated whether changes in parenting stress and the level of GMFCS in Wave 1 affected the changes in parenting stress in subsequent years through the latent growth curve model.
Statistical Analysis
A latent growth model was applied to find out how the parenting stress of mothers of children with CP changed for each participant over time. Covariance structure analysis was used to apply and analyze the latent growth curve modeling to actual data, which necessitated a sample size of at least 150 (27). The participants of this study comprised 162 children and adolescents with CP receiving rehabilitation treatment at hospitals or community welfare centers, which met the sample size for the analysis of the latent growth curve modeling.
The basic linear change model, the change model in Wave 2, and the change model in Wave 3 were first verified using the parenting stress evaluation data from the first to the third years. The suitability of the linear change in parenting stress was confirmed by comparing the fitness indices of the change models. In this study, the comparative fit index (CFI), the non-normalized fit index (NNFI or Tucker-Lewis Index: TLI), and the standard fit index (NFI), which are relative fitness indices, were used as an index. If fit indices are above .90, the model is considered to have good fit (28). Root mean square error of approximation (RMSEA) values 06–0.08 indicate reasonable. Researchers estimating models from data do not trust χ2 because the power of the χ2 test lacks (29). Therefore, the χ2 test was not used for fitness indices in this study.
After confirming the change model of parenting stress, the relationship between the change trajectory of parenting stress and the GMFCS level was investigated through multivariate latent growth modeling. For descriptive statistical analysis such as mean, standard deviation, correlation, SPSS 26.0 was used; for latent growth modeling analysis, AMOS 26.0 was used.