According to the 2011 Census, the population of Arunachal Pradesh was 1,382,611 with a density of 17 persons per km2. There are a large number of tribes in the State, and each lives in a specific geographical location. They mostly remain confined within their own communities, speak their own native language, and follow a distinct culture and tradition [18, 19].
A survey on substance use was conducted in the Changlang district of the State (1998–2000) . The population of the district was about 125,422, with 36% tribal population in the 2001 Census (see Additional file 1). The major tribes of the district are Tangsa, Singpho, Khamti and Tutsa. Of these, the Tangsa tribe has the largest population and accounts for 45% of the total tribal population in the district, followed by the Singpho tribe (7.5%), and the Tutsa and Khamti tribes (8.7%). The Tangsa mostly live together in clusters particularly at high altitude and traditionally worship supernatural powers and nature deities, but have gradually started following other religions such as Hinduism, Buddhism and Christianity. The Singpho tribe mostly lives in foothill areas close to rivers in the region, follow Buddhism, and traditionally practice meditation . Khamti is the only tribe with their own script and knowledge of the medicinal value of plants. Culturally, they are close to Singpho and follow Buddhism. Another tribe of the district is the Tutsa who live in some isolated regions toward the high hills and follow different cultural beliefs and practices. Each of these tribes lives in its own group within a geographical boundary and does not intermarry. They are distinguished by their racial appearance and colorful traditional style of dress.
A list of the census villages of Changlang district was used as the sampling frame for the substance use survey. A total of 65 villages were selected randomly and survey households in each village were selected using the method of systematic sampling. The required sample size and detailed survey plan was described elsewhere . Primary Health Center staff working in the community were trained to collect the information through a structured questionnaire. The head or most senior person of the household was interviewed to collect general household information. Individual information on opium use was recorded by interviewing each individual aged 15 years or older in the household. An individual who was currently consuming opium in any form and was a regular user for at least one month previously, was recorded as an opium user. Household members were interviewed separately to maintain privacy and accuracy of information regarding opium and other substance use, age of initiation and their relationship with other opium users in the family, if any. General information on ethnicity, religion, education, demographic and socioeconomic factors was also collected. During the survey, opium users underwent counseling by the interviewer individually and were given appropriate advice .
Sample data of 3421 individuals aged ≥ 15 years were extracted from the substance use survey (1998–2000) in Changlang district. The original data contained the records of 5135 individual respondents collected from 1092 households in 65 villages. Of these 65 selected villages, Tangsa were concentrated in 34 villages, Singpho in 11 villages, Khamti in 5 villages and Tutsas in 3 villages. The sample proportion of these tribes, e.g., Tangsa (13%), Singpho (12%), Tutsa and Khamti (10%) were similar to their proportion of the population in the district (see Additional file 1). Other tribes (Lisu, etc.) were also recorded in some samples of the villages, but they were not included in the analysis as none used opium.
Data description and analysis
Sociodemographic information, such as age, education, and occupation of respondents, was categorized to assess any association with the prevalence of opium use. Age was categorized into three groups as 15–34, 35–54 and ≥ 55 years. Occupation was categorized as unemployed, self-employed (businessman, farmer, professional) and employed (job with regular income, pensioner). The religion of the tribes was recorded as Hindu, Christian, Buddhist and Indigenous. The education of the respondents was categorized as illiterate, primary, middle, and secondary or above.
The analysis included 1795 male and 1626 female respondents with mean age ± standard deviation (SD) of 34.3 ± 16.7 years and 33.3 ± 15.3 years, respectively. Sociodemographic differences in the prevalence of opium use in the different tribes were analyzed and compared using the Chi-square test. Multivariate logistic regression analysis  was applied to identify the factors associated with opium use. Odds ratios were estimated using the multivariate logistic regression model and named as multivariate rate ratios (MRR). The variables included in the multivariate model to study the factors associated with opium use were age, education, occupation, ethnic group, marital status, religion and household size of respondents. As opium use among female respondents was low, some of the sub-groups were merged or dropped to improve the estimates of odds ratios. The data were analysed using IBM SPSS statistics for windows version 19.0 (Armonk, NY, USA).
The survey was conducted by the Regional Medical Research Centre after obtaining approval from the Scientific Advisory Committee constituted by the Indian Council of Medical Research and ethical requirements were followed. The consent of the village head was obtained before conducting the survey, as well as individual consent from the household before interview .