Bias against left-handed people is bias or design that is usually unfavorable against people who are left-handed. Handwriting is one of the biggest sources of disadvantage for left-handed people, other than for those forced to work with certain machinery. About 90 percent of the world's population is right-handed, and many common articles are designed for efficient use by right-handed people, and may be inconvenient, painful, or even dangerous for left-handed people to use. These may include school desks, kitchen implements, and tools ranging from simple scissors to hazardous machinery such as power saws.