Variables

examples include eye color, height, weight, age, political affiliation, food preference, etc. ex. birds lifespan is longer than dogs lifespan (useful) birds lifespan may be 43 years longer than dogs lifespan (more useful)
 * Variables represent a class of outcomes that can take on more than one value.**
 * The more precise the variable is measured, the more useful the measurement is.**


 * variables that have the same name may take on different values**. ex. intelligence may be measured by test scores or rank.

//__**Types of Variables**__// ex. does sleep effect the average fluency rate of students. The fluency rate would be the (measured) dependent variable.
 * Dependent variable** is the outcome of research that is being measured.

Direct control is when the researcher creates the conditions. Indirect control is when it is a naturally occurring.
 * Independent variable represents conditions that the researcher has direct or indirect control of to test their effects on the outcome. The independent variable may be manipulated at different levels.** ex. does sleep effect the average fluency rate of students. The amount of sleep may be the controlled or independent variable. The environment of sleep may be an additional level.

//A general rule to follow is when groups or characteristics are being assigned or manipulated, that variable is independent.//

Independent variables must take on at least two **levels of values**. ex. if gender difference in job performance was to be measured, you must study the two levels of gender.

//**The best independent variable is one that is** **independent of any other variable that is being used in the same study.**// the study then contributes the maximum amount of understanding beyond what other independent variables can offer. //**When variables compete to explain effects, it is called confounding.**//
 * The Relationship Between Independent and Dependent Variables**
 * //The best dependent variable is one that is sensitive to changes in the different levels of the independent variables.//** otherwise you man never know the effect of the treatment or condition.

A **Control Variable** is one that **//may have potential influence//** on the dependent variable, so it needs to be controlled. ex. intelligence levels may influence the outcome of study on relationship between fluency and comprehension. An **Extraneous Variable** is a variable that //**may have an unpredictable effect**// on the dependent variable. ex. When studying the effect of television, the type of program may have a positive or negative impact on the dependent variable. A **Moderator Variable** is one that is //**related to**// the dependent or independent variable, //**masking their relationship**//. Ex. examining crime rate with ice cream consumption, you need to factor in temperature or conclusions may be inaccurate.