1. IntroductionPadang is the capital of Indonesia’s West Sumatra province and lies on Sumatra’s west coast with a width of 694.96 km. Padang city consists of 11 districts and 104 villages [1] . The population of the community in Padang is 856,815 people who consist of 423,039 men and 433,776 women and the human growth index is 2.31% per year. The biggest age group is 15 - 64 years old with a proportion of 68%. The level of education above high elementary school (SMU) was only 2847 people [1] .
Earthquakes were higher than 6 on the Richter scale happened many times in West Sumatera in a period of time from January 2009 to August 2011 [2] . The highest magnitude of earthquakes that occurred in Padang and West Sumatera on Wednesday, 30th September 2009 at 5:16 pm at local time which had a magnitude of 7.9 on the Richter scale. The epicenter was 45 kilometers (28 miles) in the west-northwest of Padang, Sumatera [2] . The impact of the earthquake was felt not only by adults but also by children and adolescents who had worries, anxiety, fears and even depression or stress [2] . One form of psychological effects often encountered in the adolescent disaster victims after the earthquake was Post Traumatic Stress Disorder (PTSD). The government of Indonesia reported that 1195 people were killed, 1214 were seriously injured and 1688 suffered minor injuries. Most of the deaths occurred in the Padang Pariaman area (675 people), Padang (313 people), Agam (80 people) and the city of Pariaman (37 people). In addition, around 135,000 houses were severely damaged, 65,000 houses were damaged and 79,000 houses were partially damaged. An estimated 250,000 families (1,250,000 people) have been affected by the earthquake [2] .
PTSD is a disorder that is caused by traumatic events that threaten the safety of someone or make someone powerless [3] . National Institute of Mental Health (NIMH) defines PTSD as a type of anxiety disorder that occurs after trauma or traumatic events [4] . High magnitude of earthquake can cause secondary stressors (psychosocial loss, decrease in academic performance, media terror, etc.).
Not all earthquake survivors suffered PTSD. It depends on the factors that influence them. One of these factors is the cognitive factor that consists of coping strategies and self-efficacy. Self-efficacy means how one’s perception has the potency and ability to influence their own behavior, motivations, thoughts and emotions during stressful situations [5] . Self-efficacy was believed to aid the person during a period of stress. With confidence, adolescents will be able to face their future life. Any obstacles and challenges they faced and all of the issues that matter will be able to be overcome by them. Having good self-efficacy, especially for the adolescents can help them in becoming optimistic and courageous in life.
Coping ability is the attempt by the individual to manage external and internal demands that were caused by sources of stress [6] . Coping abilities are special efforts, both behavioral and psychological, which are used by the individual to master, tolerate, reduce or minimize the impact of stressful events. Good coping abilities are required for adolescents to allow them to solve their problems correctly [7] . The present study aimed to determine the prevalence of PTSD and its association with coping strategies and self-efficacy among adolescents living in the earthquake prone area of Padang, West Sumatera Province, Indonesia. According to the World Health Organization (WHO), adolescents include those who are of 10 - 19 years of age [8] . The law of Indonesian Republic No. 23/2002 stated that the age of adolescents defined as 10 - 18 years old [9] .
2. Methodology2.1. Study Design and Sample PopulationA population-based cross-sectional study was conducted in Padang Sumatera Indonesia; 32 months post highest magnitude of earthquake day in Indonesia which was the 30th September 2009. This area is known to have frequent small scale earthquakes on-going as it is located in the tectonic slab between two major plates of Eurasian and Indo Australian plates. The research was conducted on the junior and senior high schools in Padang which are located in the earthquake-exposed area. These schools were reported having psychosocial problems among their pupils after earth quakes on 30th September 2009 and 26th October 2010 with 7.9 on the Richter scale and 6.8 on the Richter scale respectively [2] . The sample in the present study consisted of all students who were born in 1994- 2000 and were exposed directly to the earthquake event stated. The population of the group aged 10 - 19 years old reported was 172, 175 adolescents [2] .
2.2. Sample Frame, Sampling Unit and SampleThe sampling frame consists of a list of schools involved in the earthquake-ex- posed area (Figure 1). The data regarding the severity of destroyed school buildings were obtained from the educational department ministry in Padang to group into clusters of mild, moderate and severe clusters. From each cluster which was based on severity of damaged building, only one school was selected for each cluster. Therefore, there were 3 schools represented for junior and 3 schools represented for senior high schools. The junior schools represented for adolescent of age 12 - 15-year-old and the senior schools represented for 16 - 19 years old adolescents. From selected schools, one class was randomly selected by the school counsellor and all adolescents from the selected class were chosen as participants. The inclusion criteria were; the adolescent who was born in 1994- 2000, exposed to the earthquake on 30th September 2009 and stayed in Padang during data collection period. The minimal sample size was estimated using calculated PS2 Sample size with Fleiss JL (1981) method [10] . The calculated result was based on factors that determined PTSD among adolescents [11] , with a confident interval of 95% and power of 80%, the sample size required was 720 adolescents. The methodology flow chart was shown as in Figure 1.
2.3. Study InstrumentsThe instrument used was the self-administered questionnaire consisted of 3
parts. Validated questionnaires used obtained with permission from several sources, including the local validated questionnaire [12] . The first and second part was focused on the information about adolescent characteristics, such as gender, age and family status. The second part consisted of measurements for PTSD in adolescents using 17 items for typical symptoms of PTSD according to the B, C and D criteria listed in DSM-IV using a revised University of California, Los Angeles Reaction Index (UCLA-RI) questionnaire [13] . The questionnaire was translated into Indonesian language. Validation done at pretest found that the internal consistency (r) > 0.195, alpha Cronbach > 0.8. The PTSD consists of three clusters symptom; re-experiencing, avoidance/ numbing and hyper-arousal symptoms. UCLA-Adolescent Version was used to measure symptoms of PTSD (17 items questionnaire with scale 0 - 4) with ranging from none problem, coded as 0, to a lot of problems coded as 4. The third part covered the psychosocial loss exposure to the earthquake assessed by a property destruction index with 6 items [11] and the coping strategy consisted of 5 items [14] . The validation for internal consistency on sub-variables of approach coping and also avoidance coping showed that both had r > 0.195 and the range of Alpha Cronbach of 0.7 - 0.8. Questionnaire for self-efficacy was derived from Coppel’s self-efficacy scale [13] . After validation, these items showed that the internally consistent with r > 0.195 and alpha cronbachs of 0.8. The questionnaire for psychosocial loss was modified from Strand et al. [14] and Wickrama et al. [15] with only 9 items used. The validation for validated with Cronbach α coefficient ranged from 0.65 to 0.75. To measure the trauma post-earthquake, the Earthquake Trauma Questionnaire of 14 items were used.
The conduct of the present study has been approved ethically by Universiti Kebangsaan Malaysia research ethic committee and permission to run this study has been obtained prior to data collection period.