This cross-sectional study was done in accordance with the declaration laid by, declaration of Helsinki (revised 2013) for recruiting human subject and Bangladesh medical research council guideline 2014. Ethical permission was obtained from the institutional ethical review board of Mount Adora Hospital (MAH/ERB: 02/2020) and departmental ethical review board of Maharishi Markandeshwar university, (IEC-1215) Solan, Himachal Pradesh, India. A digital consent was obtained from each participant after brief description of the purpose of the study putting a separate section in the form by asking a question “do you agree to undergo in this study?” The design of the study, data collection procedure, presentation of the data, and citation comply with the standard Committee on publication Ethics (COPE) guideline.
Subject and procedure
A cross-sectional study was done among physiotherapy students in Bangladesh and India between the 20th January 2020 and the 25th February 2020. Simple random sampling method was used to recruit the required sample. Study sampling population was recruited by listing the students of two different universities in Bangladesh and India from the department of physiotherapy. A random sampling technique was used by using computer-generated random number generator from the sample population of 665 students to make a sampling frame of 326 students identifying according to the pre-fixed inclusion and exclusion criteria from the recognized university.
Subject recruitment criteria
This cross-sectional study comprised of both male and female participants. The required subject selection criteria included candidates age group between 18 and 30 years, who were able to understand the English language to fill up the questionnaire and willing to give consent to participate in this study. The exclusion criteria were any known condition which could lead to pain in the neck or upper limb, recent fracture in neck and upper limb, any traumatic injury to neck and upper limb prior 6 months, congenital abnormalities and severe surgical and neurological disorders.
Sample size estimation
The subjects size was calculated by utilizing the formula for estimating proportion: n = Zα2 P (1 − P)/d2, where Zα = 1.96; P = 75.8%; from the previous published article , and d = 5%. The study required a minimum of 326 participants. We did not expect 10% incomplete form as we have set the option required in every question in Google forms.
Demographic characteristics such as gender, age, weight, height, body mass index (BMI), year of study, duration of owing a smartphone, daily smartphone usage time, purpose of smartphone use in a typical day such as text messaging, social networking, watching videos, and gaming were included.
Smartphone addiction scale–short version (SAS-SV)
The SAV-SV is a 6-point Likert type scale containing 10 questions. The scale starting from 1 (strongly disagree) to 6 (strongly agree). The overall score ranges from 10 to 60. Higher score indicates high risk of smartphone addiction. The scale is valid and reliable to measure smartphone addiction. The internal consistency of SAS-SV was verified by Cronbach’s alpha of 0.911 among adolescent population 
Neck Disability Index (NDI)
The NDI is a widely used valid and reliable instrument to measure neck pain. The questionnaire has involved a 10-item Likert scale ranging from 0 (no pain) to 5 (worst pain). The total score ranges from 10 to 50, where high score indicate severer neck disability. The intra class correlations value of NDI is in between 0.50 and 0.98 indicates good validity and reliability of the tools .
Shoulder Pain and Disability Index (SPADI)
The shoulder pain and disability index is used to measure shoulder pain and disability is a 13-item scale that have two domains; 5 items subscale measured pain and 8 item subscale measured disability on a numeric pain rating scale. The total score ranged from 0 to 140 was expressed as a percentage. The percentage score ranged from 0 to 100, where a greater score represented more disability . The test-retest reliability of SPADI was ranged from 0.64 to 0.66 and internal consistency range from 0.8604 to 0.9507 .
Oxford elbow score
A 12-item questionnaire was reported to measure elbow pain and function. Each item responses were scored from 0 to 4 Likert scale. The total sum score of all items were used for analysis. The Cronbach’s alpha 0.92 showing excellent reliability of this scale .
Cornell Hand Discomfort Questionnaire (CHDQ)
The CHDQ is a valid and reliable tool to measure pain in the hand. The questionnaire contains three domains including experience of pain, discomforts of pain, and interference of pain. The total discomfort score was calculated as frequency × discomfort × interference. The maximum score of one shaded area of one hand is 45 and total score of the six shaded area is 270. We ask the participants to fill-up the questionnaire for only domain hand. The validity of the questionnaire was established by Erdinc et al. reported the Kappa coefficients, which is ranging from 0.56 to 0.97 indicated moderate to good test-retest reliability .
Survey validation and administration
The draft of the survey questionnaire was not subjected to content validation as the tool we used was an already validated tool. The final draft of the questionnaire was tested initially on five representative population to check the response time; it took no more than 20 min to complete the questionnaire. From the sample frame of 665 population, 326 potential participants were selected by simple random sampling method from two reputed Universities of Bangladesh and India. Face-to-face data collection was carried out during the break time of the students’ college hour. We utilized Google Forms® platform to collect the survey response as it is echo friendly. The enrolled student’s contact details was obtained and the survey link was send to the participant’s either WhatsApp, Messenger, or text message through the smartphone. Google Forms prevents the incomplete submission by putting the option required in every question.
Data analysis was carried out by using SPSS 20.0 software for windows. The continuous variables are presented as mean and 95% confidential interval. Categorical variables are presented as number and percentage. Between groups analysis was conducted by using Mann-Whitney U test. Association between SAC and NDI, SPADI, OES, and CHDQ was measured by using chi-square test.