Femicide is defined as the systematic killing of women for various reasons, usually cultural. The word is attested from the 1820s. According to the United Nations, the biologically normal sex ratio at birth ranges from 102 to 106 males per 100 females. However, ratios higher than normal – sometimes as high as 130 – have been observed. This is now causing increasing concern in some South Asian, East Asian, and Central Asian countries. Such disparities almost always reflect a preference for boys as a result of deeply embedded social, cultural, political and economic factors.