of political science, Michael Gunter wrote that Kurdish sources tend to exaggerate numbers, while the states that Kurds live in often undercount the Kurdish population. Their numbers are estimated at 14,000,000 people by the CIA world factbook (18% of population). A report commissioned by the National Security Council (Turkey) in 2000 puts the number at 12,600,000 people, or 15.7% of the population. One Western source estimates that up to 25% of the Turkish population is Kurdish (approximately 18-19 million people). Kurdish nationalists put the figure at 20,000,000 to 25,000,000. All of the above figures are for the number of people who identify as Kurds, not the number who speak a Kurdish language, but include both Kurds and Zazas. Estimates based on native languages place the Kurdish population at 6% to 23%; Ibrahim Sirkeci claims the closest figure should be above 17.8%, taking into account political context and the potential biases in responses recorded in surveys and censuses. The population growth rate of Kurds in the 1970s was given as 3.27%. According to two studies (2006 and 2008) study by KONDA, people who self-identify as Kurdish or Zaza and/or speaks Kurmanji or Zazaki as a mother tongue correspond to 13.4% of the population. Based on higher birth rates among Kurdish people, and using 2000 Census results, KONDA suggested that this figure rises to 15.7% when children are included, at the end of 2007. Since the immigration to the big cities in the west of Turkey, interethnic marriage has become more common. A 2013 study estimates that there are 2,708,000 marriages between Turks and Kurds/Zaza. Turkish government statistics show that Kurdish women in Turkey give birth to about four children, more than double the rate for the rest of the Turkish population. The Kurdish population is growing, while the rest of the country has birth rates below replacement level. In some Kurdish dominated provinces women give birth to 7.1 children on average. Women in Kurdish dominated provinces of eastern Turkey also have an illiteracy rate about three times higher than men, which correlates with higher birth rates. In 2000 66% of 15-year-old girls from Şırnak Province could not read or write. Language The majority of people who identify as Kurds speak Kurmanji, meanwhile a minority of them speak Turkish or Zazaki as their mother language. A study published in 2015 that demographically analysed the Kurdish inhabited regions of Turkey (excluding diaspora) concluded