Reference interval

A reference interval (sometimes called a reference range or normal range) describes the range of values of a measured quantity in healthy individuals.

• Reference limits
  A reference limit defines a value where a given proportion of reference values are less than or equal to. A reference interval defines the interval between a lower and upper reference limit that includes a given proportion of the reference values.
• Histogram
  A histogram shows the distribution of the data to assess the central tendency, variability, and shape.
• Box plot
  A box plot shows the five-number summary of the data – the minimum, first quartile, median, third quartile, and maximum. An outlier box plot is a variation of the skeletal box plot that also identifies possible outliers.
• Normal probability (Q-Q) plot
  A normal probability plot, or more specifically a quantile-quantile (Q-Q) plot, shows the distribution of the data against the expected normal distribution.