One explanation given inside Bhutan is that the higher CIA numbers ultimately trace back to an inflated population number the Bhutanese government supplied to the United Nations in the early 1970s in order to gain entry into that body (the UN reportedly had a cutoff population of one million at that time -- see micronation for justifications in support of such a minimum). According to this theory the CIA population experts have retained this original inflated number year after year while adjusting it each year for normal population growth.
An alternative theory is that the western and central districts of the country wish to underestimate the populations of the southern and eastern districts in order to maintain their historical dominance over those districts. This is the claim made by some Bhutanese refugee groups. Certainly the government numbers do not include people in the refugee camps in Nepal and other persons forced out of Bhutan, which total approximately 125,000.
The Bhutanese numbers can be reconstructed from their 9th Five Year Plan documents , which lists the exact number of households in each gewog. If the Bhutanese refugee advocate groups are correct, a spot check of a southern gewog should show a massive under-reporting of population (although this would have to be done by a non-interested party to have credibility).
Approximately two-thirds to three-quarters of the population practice Drukpa Kagyupa or Ningmapa Buddhism, both of which are disciplines of Mahayana Buddhism. Approximately one-quarter of the population is ethnic Nepalese and practice Hinduism. They live mainly in the south and follow the Shaivite, Vaishnavite, Shakta, Ghanapathi, Puranic, and Vedic schools. Christians both Roman Catholic and Protestant and nonreligious groups comprised less than 1 percent of the population. Bön, the country's animist and shamanistic belief system, revolves around the worship of nature and predates Buddhism. Very few citizens adhere exclusively to this religious group.