Population policies aim to influence population size, growth, distribution or composition through incentives or deterrents. China has operated the strictest population control policy since 1979 through its one-child policy, which aims to control natural increase. The one-child policy has been most effective in urban areas and has significantly reduced China's population growth, preventing over 300 million births. However, it has also led to negative social consequences like an aging population and skewed sex ratios with more boys than girls. While some praise its role in China's economic growth, many see it as a violation of civil liberties.