This method is no longer in general use because it has some significant flaws, chiefly that after childhood raw scores don't proportionately increase with chronological age. Nowadays the term IQ generally describes a score on a test that rates the subject's cognitive ability as compared to the general population, using a standardized scale with 100 as the median score. On most tests, a score between 90 and 110, or the median plus or minus 10, indicates average intelligence. A score above 130 indicates exceptional intelligence and a score below 70 may indicate mental retardation. Like their predecessors, modern tests do take in to account the age of a child when determining an IQ score.
Children are graded relative to the population at their developmental level.
Simply put, IQ tests are designed to measure your general ability to solve problems and understand concepts. This includes reasoning ability, problem-solving ability, ability to perceive relationships between things and ability to store and retrieve information. IQ tests measure this general intellectual ability in a number of different ways. Most people perform better on one type of question than on others, but experts have determined that for the most part people who excel in one category do similarly well in the other categories, and if someone does poorly in any one category, he also does poorly in the others. Based on this, these experts theorize there is one general element of intellectual ability that determines other specific cognitive abilities.