What is a variable? List at least five different variables and then describe at least two levels of each variable. For example, age is a variable. For adults, age has values that can be expressed in years starting at 18 and ranging upward. In an actual study, the age variable might be measured by asking for actual age in years, the year of birth, or providing a choice of age ranges such as 18–34, 35–54, and 55+. Sentence length is a variable. The values might be defined by the number of words in sentences that participants write in an essay.