Answer: The Edinburgh Inventory is a psychological examination that quantifies a person's hand dominance.
Most people are right hand dominant. This means that they prefer to perform tasks with their right hand rather than their left. About 70 to 95% of people express this right hand dominance.
The Edinburgh Inventory is a self-report questionnaire to assess how dominant a person is with one of their hands. It can be easily conducted with a computer. It is a very short form, and is easy to score and evaluate.
The Edinburgh Inventory of Handedness was first published by R.C. Oldfield in 1971 in the journal Neuropsychologia.
The tasks assesses all range of activities. Precise, fine motor skills are evaluated by asking which hand is used in writing or drawing. Additionally, handedness dominance of ballistic actions are measured by asking about throwing. Other questions that appear on the index include behaviors such as using a toothbrush, striking a match, holding the lid while opening a small box, and the top hand while using a broom.
There has been a major revision to the original Edinburgh handedness inventory. Researchers found that the original 10 question index did not have a good fit with the data. In its place, they offered a revised 4 question survey that was better at determining handedness. These results were published in the journal Laterality (Edinburgh Handedness Inventory - Short Form: a revised version based on confirmatory factor analysis)
The output of the Edinburgh Inventory is a "laterality index" or LI (sometimes called a "laterality quotient.") The laterality index is a number from -100 to 100. A person who does all functions entirely with their right hand will receive a laterality index of 100, while a person who uses their left hand exclusively will receive a -100. A person who is purely ambidextrous and performs all functions equally well with both hands receives a 0.
From here, the population is divided into deciles. Generally, the 10% with the most right handed dominance use their right exclusively.