Sample size calculation
The formula was used to calculate sample size: \(\text{n}=\frac{(1+1/\text{c})\text{p}\text{q}{\left({\text{Z}}_{{\alpha }}{\text{Z}}_{{\beta }}\right)}^{2}}{{\left({\text{p}}_{1-}{\text{p}}_{0}\right)}^{2}}\), where P1 = \(\frac{{ORP}_{0}}{1+{P}_{0}(OR-1)}\),‾p = \(\frac{{\text{p}}_{1}+\text{c}{\text{p}}_{0}}{1+\text{c}}\),‾q = 1 -‾p, \({ \text{Z}}_{{\alpha }}\)= 1.96, \({\text{Z}}_{{\beta }}\)= 1.282. According to the previous study (P0 = 0.2365, OR = 2)[14], the sample size of case group was 98. Moreover, a rough estimation by multiplying the sample size by 1.1 to 1.2 times to reduce the sampling error.
Participant recruitment
The study was approved by the medical ethics review board (QYFY WZLL 25896). The study was conducted in the Children Preventive Health Care Clinic of a tertiary hospital in an east coastal city of Shandong Province, China. Children and their parents, who were seeking primary care services at the Children Preventive Health Care Clinic from August 2020 to May 2021, were invited to participate in the study. Written informed consent for participation was obtained from parents. Inclusion criteria were as follows: (1) children diagnosed as FC by pediatric Rome IV criteria; (2) children aged between 2 and 6 years; (3) parents aged ≥ 18 years; and (4) parents with literate and able to complete the questionnaire themselves. Exclusion criteria were as follows: children (1) with other diseases that cause constipation, such as congenital megacolon; (2) with other serious diseases, such as hematological and neoplastic disorders; and (3) participated in other clinical trials. There were 116 children and their parents who were eligible for enrollment in the study, and eight children were excluded because children's parents did not complete the questionnaire. Finally, data from a total of 108 children were analyzed. Taking children's age as the matching factor, 324 parents of healthy examination children without FC were selected in the same clinic and the same period at a ratio of 1:3 as the control group based on the reported FC incidence data in China[14]
.Questionnaires were collected by trained investigators in the form of face-to-face interviews. Parents were asked to complete the questionnaire for their children. Prior to the survey, the investigators explained the purpose of the study to the participants. Each survey took about 20 min to complete. To avoid missing data, the investigators checked the questionnaires one by one and asked the parents to fill in the missing items with their willingness.
Measures
Children's parents completed the following 5 questionnaires: General information questionnaire, the Parental Conflict Scale, the Parenting Style Questionnaire, the Child-parent Relationship Scale and the Children's Emotional Adjustment Scale-Preschool Version.
General Information Questionnaire
Based on literature review and consulting experts in the field of child health care and gastroenterology, a general information questionnaire was designed. The questionnaire included three parts: (1) demographic information about age, gender, birth order, family type, mother's working status, monthly household income and parent's highest level of education; (2) children's factors including food allergy, poor appetite, and bowel habits, etc; and (3) family related factors including parents' history of constipation, interaction time between parents and children, etc.
The Parental Conflict Scale
The Parental Conflict Scale (PCS) was used to evaluate the intensity of parental conflict, which was designed by Chen et al [15] in 2015. It includes 5 items, which are self-evaluated by parents and has been widely used as a validated tool in various studies with good reliability and validity. Items are scored on a five-point Likert scale, which ranges from 0 (completely disagree), not at all to 5 (completely agree), with higher scores indicating higher parents conflict. The internal consistency was good in this study (Cronbach's alpha 0.859).
The parenting style questionnaire
The parenting style was measured using the Chinese version of the parental style questionnaire, which was designed by Yang[16].This instrument includes 40 items in five subscales: doting, permissive, authoritarian, democratic and inconsistent parenting style. Items are scored on a five-point Likert scale, ranging from 1 (never) to 5 (always). The higher score of the subscale indicates more popularity of parenting style in the subscale. The questionnaire demonstrated an acceptable internal consistency with Cronbach's alpha value of 0.879 and the subscales varied from 0.808 to 0.944 in the current study.
The Child-parent Relationship Scale
Child-parent relationship was assessed through the Child-parent Relationship Scale (CRS), which was translated and revised by Zhang et al[17]. CRS is a 26-item scale that includes three dimensions: intimacy, dependence and conflict. Zhang et al[17] reported that the reliability of dependency dimension was low, thus only two dimensions of intimacy and conflict were used in the present study. Items are scored on a 5-point Likert scale, with higher scores indicating higher intimacy or conflict in the child-parent relationship. The Cronbach's alpha was 0.812 for the total scale and was 0.802 and 0.905 for the two dimensions, respectively.
The Children's Emotional Adjustment Scale
The Children's Emotional Adjustment Scale-Preschool version (CEAS-P) was used to measure the ability to regulate key emotions such as anger, fear and shyness of children. The scale was revised by Wu et al[18] in 2020. CEAS-P includes 29-item on three dimensions of temper control, social assertiveness and anxiety control. The items are scored on a 5-point Likert scale, with 1-5 points from "never" to "always". The Cronbach's alpha was 0.937 for the total scale and was 0.906-0.925 for the three dimensions.
Statistical Analysis
All statistical analyses were performed using Statistical Package for Social Sciences (SPSS) version 21.0. Measurement data with normal distribution were presented as mean ± SD, and t test was used for comparison between groups. Categorical variables were presented as frequency and percentage, and Chi-squared test or Fisher exact tests were applied for non-grade data comparison and Wilcoxon rank sum tests were applied for grade data comparison. Logistic regression analysis was used to determine independent risk factors for FC in preschoolers based on the Wald statistics using backward stepwise progression. All risk factors with P < 0.05 were included in the multivariate predictive model. GraphPad Prism software 9.0.2 was used to plot the regression forest map.