The interval level of measurement involves assigning scores on a numerical scale where the intervals between values have the same consistent interpretation throughout. For instance, the difference between $30$ and $40$ degrees Fahrenheit represents the same amount of temperature change as between $80$ and $90$ degrees. In psychology, the intelligence quotient (IQ) is measured at the interval level; the difference between IQ scores of $80$ and $100$ is the same as between $120$ and $140$. However, interval scales lack a true zero point that indicates the complete absence of the measured quantity, meaning it is not meaningful to compute ratios of these scores. Furthermore, interval-level measurement permits any indicators of central tendency to be computed, including the mean, median, or mode.