Study design, period, setting, and population
An institutional-based cross-sectional study was conducted in Dilla University from May1st 2019 to June-1 2019, located in south of the capital city of Ethiopia and far by 360 Km. One of the newer universities that was founded in 1996 G.C was named as Teachers and Health Science College in Ethiopia. However, since 2007 G.C, it is providing higher level of education in many disciplines, which has been clustered into three campuses and six colleges. Currently, it has 47 undergraduate and 17 postgraduate departments, at BA/ BSc, Bed, MA/MSc level with regular, extension, and summer courses, and it has about 30108 students. The study population was randomly selected undergraduate students of Dilla University.
Sample size determination
The minimum number of samples required for this study is determined by using Single population proportion formula considering the following assumptions:

Where
n = minimum sample size required for the study
Z= standard normal distribution (Z=1.96) with confidence interval of 95% and ⍺=0.05
P= the prevalence of internet addiction is not known in our country; hence, P= 50 % (0.5) was used.
d= Absolute precision or tolerable margin of error (d) =5%=0.05

Then adding 10% (384 x 0.1 = 38.4 ≈ 39) of non-respondent the total sample size for this study is 384+39=423. And finally, by using the design effect the above sample size is multiplied by finally by using the design effect the above sample size is multiplied by 2 = 846. We used a multistage cluster sampling procedure to select sample of undergraduate students. Initially, two colleges (College of medicine and health sciences, and College of business and economics), and one school (school of law) were selected. In the second stage, the selected college is stratified based on the departments. There are thirteen (13) departments on the selected college. All thus departments with their years of student was included in this study and also design effect was used. The final sample size was allocated proportionally for each department based on the number of their students. Finally, simple random sampling technique was used to select participants by using their ID number as a sampling frame.
Data collection tools and procedures
Data was collected by using self-administered structured questionnaire. The self-administered structured questionnaire consists of the 88 items with closed ended questions. The questionnaire is divided into seven (7) sections; Socio-demographic characteristics (has 9 items), Internet addiction test (20 items), Self-esteem factors (10 items), Depression and anxiety (14 items), Social support scale (3 items), Peer Influence (29 items) and Current substance use (3 items).
Data on the components of internet addiction was collected by using Young‟s internet addiction test (IAT). This scale has been widely used for screening and measuring the level of internet addiction worldwide and YIAT showed that it is more reliable in University students. The Generally Cronbach α in the present study was 0.89. Each item of the YIAT 20 is rated on a scale from rarely to always. Using a five-point Likert scale, the responses were assigned a numeric value or score where ‘rarely’ was scored one point and ‘always’ was scored five points. These items include questions about compulsive behavior related to the use of internet, presence of problems in academic performance, bad home environment, relationship problems with family or friends, and suffering from emotional problems. After answering all the questions, scores of each response are added to obtain a final score ranging between 20 and 100.The higher the score, the greater the level of addiction. There is no gold standard for distinguishing between IA and non-IA. According to the IAT manual, users are given four labels based on the total score, normal user (score ≤20), mild user (score between 20 and 49), moderate user (score between 50 and 69), and severe or excessive user (score ≥80)(26). Since the moderate users are often unable to control their internet use, we considered both moderate and excessive use of internet (IAT total score ≥50) as IA and also based on the IA test manual, we considered that those who scored between 0 and 49 were normal users of internet. This opinion of internet addiction classification is fairly supported by the existing literature (18, 27, 28).
Rosenberg Self-esteem scale was used to assess self-esteem. It was measured with10-item scale that measures global self-worth by measuring both positive and negative feelings about the self. The scale is believed to be uni-dimensional. All items are answered using a 4-point Likert scale format ranging from strongly agree to strongly disagree(29).
Peer pressure was measured by PPQ-R which is a 29-item self-report scale that assesses peer influences in everyday life situations. It is a 5-point Likert scale with 1 (strongly disagree) to 5 (strongly agree). The scale consists of five subscales and high score on each subscale indicates higher peer pressure in that form(30).
Hamilton Anxiety Rating Scale (HARS)-was one of the first rating scales developed to measure the severity of anxiety symptoms, and is still widely used today in both clinical and research settings. The scale consists of 14 items. Each item is scored on a scale of 0 (not present) to 4 (severe), with a total score range of 0–56, where <17 indicates mild severity, 18–24 mild to moderate severity and 25–30 moderate to severe(31).
Hamilton Depression Rating Scale (HDRS) - is the most widely used clinician-administered depression assessment scale. The original version contains 17 items (HDRS17) pertaining to symptoms of depression experienced over the past week. For the HDRS17, a score of 0–7 is generally accepted to be within the normal range (or in clinical remission), while a score of 20 or higher (indicating at least moderate severity) is usually required for entry into a clinical trial(32).
Social support was measured using Oslo 3 items social support scale (OSS-3) which is poor social support- a score of “3-8” ,intermediate social support- a score of “9-11” ,strong social support- a score of “12-14” (33).
Data quality control issues
Training was given to the data collectors and supervisors on the data collection tool and sampling techniques. Supervision was held regularly during the data collection period both by the researcher, co-investigators and supervisors to check on a daily basis for completeness and consistency. In addition, pre-test of the study was carried out in 5 % (43) of total undergraduate students at outside of the study area (Hawassa University), which is closer to the study area.
Analysis
Following accomplishment of data collection activities, the questionnaires was entered in to EpiData version 3.1, (where QES, REC and Check files created), to ensure a double data entry system and then, was exported to SPSS version 22, to accomplish further data exploration procedures; along with the required statistical data analysis methods. Descriptive statistic (mean, median, frequency, and percentage) was used to summarize data and the result was reported using frequencies, percentages, charts, and tables. Bivariate and multivariate logistic regression analysis was conducted to identify factors associated with internet addiction and statistically significant was considered at P-value <0.05.