Estimates of prevalence of<unk>  have ranged widely, from 1 in 4 to 1 in 25,000–100,000. However, most studies have relied on synesthetes reporting themselves, introducing self-referral bias. In what is cited as the most accurate prevalence study so far, self-referral bias was avoided by studying 500 people recruited from the communities of Edinburgh and Glasgow Universities; it showed a prevalence of 4.4%, with 9 different variations of<unk> . This study also concluded that one common form of<unk>  grapheme–color<unk>  (colored letters and numbers) is found in more than one percent of the population, and this latter prevalence of graphemes–color<unk>  has since been independently verified in a sample of nearly 3,000 people in the University of Edinburgh. The most common forms of<unk>  are those that trigger colors, and the most prevalent of all is day–color. Also relatively common is grapheme–color<unk> . We can think of "prevalence" both in terms of how common is<unk>  (or different forms of<unk>  within the population, or how common are different forms of<unk>  within synesthetes. So within synesthetes, forms of<unk>  that trigger color also appear to be the most common forms of<unk>  with a prevalence rate of 86% within synesthetes. In another study, music–color is also prevalent at 18–41%. Some of the rarest are reported to be auditory–tactile, mirror-touch, and lexical–gustatory. There is research to suggest that the likelihood of having<unk>  is greater in people with autism spectrum condition.
Synesthesia
Dysesthesia
Hypoesthesia
Hyperalgesia
Hypoalgesia
Pallesthesia
Chromesthesia
Neuralgia