The present study was a cross-sectional study conducted on students from different schools of Mazandaran university of medical sciences. Overall, 358 university students were recruited through stratified random sampling. Data were collected using a demographic questionnaire, a cell phone use questionnaire, Pittsburgh sleep quality index (PSQI), and the Social readjustment rating scale. All individuals participated voluntarily in the study. The students first received instructions on each questionnaire in their classrooms, and were then handed out the questionnaires. The students were reassured that their personal information would remain confidential, and they were asked to complete and return the anonymous questionnaires, if they were willing to participate.
The completed questionnaires were collected by a colleague researcher. The SPSS® 13.0 software for windows was used to analyze the data. Descriptive indices were used to express data, and the chi-square and logistic regression were used to interpret the results.
The cell phone use questionnaire was used by Van den Bulck in 2007. It evaluates the use of cell phones by adolescents after lights are out and its relationship with fatigue. In the present study, we used the Persian translation of this questionnaire for students of Mazandaran University of Medical Sciences. The face validity of the Persian version was confirmed by professors at the psychiatry and behavioral sciences research center, and its reliability was verified through test-retest reliability (interval of two weeks) with a subset of 20 students (P = 0.001; r = 0.94).
The Pittsburgh sleep quality index (PSQI) has been developed to measure sleep quality during the previous month. A post hoc cutoff score on the PSQI produced a sensitivity of 89.6% and a specificity of 86.5% (16, 17). This questionnaire has been previously used in Iranian studies and its validity and reliability have been confirmed (18).
The Social Readjustment Rating Scale was first devised by Holmes and Rahe (19). They made the assumption that each event, whether positive or negative, requires some sort of adjustment, to devise a checklist of 43 stressful events, which was used in the present study.