Table 2.

Descriptive statistics and correlations among key variables and covariates

	1	2	3	4	5	6	7	8
1. PSU	–
2. MPUT-Learning	−0.08	–
3. MPUT-Entertainment	0.06	0.67	–
4. MPUT-Communication	0.13	0.61	0.71	–
5. Instrumental motivation	−0.22	0.14	0.02	0.00	–
6. Self-expression motivation	0.10	0.21	0.14	0.09	0.25	–
7. Social relationship motivation	0.09	0.15	0.12	0.09	0.25	0.49	–
8. Hedonic motivation	0.21	0.17	0.18	0.14	0.23	0.58	0.64	–
Covariates
Age	−0.03	0.04	0.20	0.16	0.09	0.05	0.03	0.07
Gender	−0.13	−0.06	−0.09	−0.11	0.01	−0.14	−0.07	−0.11
Grade	−0.05	0.08	0.19	0.14	0.08	0.04	0.02	0.07
Relationship	−0.08	−0.13	−0.10	−0.15	−0.01	−0.17	−0.05	−0.12
Parent's age	−0.05	0.01	0.09	0.03	0.15	0.06	0.01	0.04
Educational level	−0.01	0.10	0.01	−0.03	0.14	0.20	0.16	0.18
District location	0.05	0.11	0.12	0.05	0.05	0.10	0.05	0.08
District type	0.09	−0.02	0.07	0.04	−0.15	−0.14	−0.09	−0.08
Family annual income	−0.01	0.12	0.17	0.02	0.22	0.12	0.16	0.17
Mean	3.60	0.13	0.13	0.13	3.80
SD	2.61	0.13	0.13	0.14	1.09
n	7,292	3,420	6,556	4,397	7,292

Note: Bolded coefficients were significant at P < 0.05 (two-tailed) level; the factor scores of the latent variables were computed by adding the products of their corresponding items and the factor loadings of the items; PSU, problematic smartphone use; MPUT-Learning, smartphone use time for learning; MPUT-Entertainment, smartphone use time for entertainment; MPUT-Communication, smartphone use time for communication.