Basic to any analysis of left-handedness is a working definition of handedness. Left-handedness and right-handedness must be defined in standard terms. The layperson tends to focus upon handedness as the sole factor of sidedness. It is important to realize that left-eyedness, left-footedness, and left-earedness exist. Therefore, sidedness is a function of all these factors, and scientists use questionnaires that measure sidedness. For example, one question might be: which eye would you use to look through a keyhole? Research on the validity of these questionnaires suggests that the accuracy of the questionnaire depends on how the question is phrased. The most widely used test is the Edinburgh, Oldfield, Handedness Inventory. The test is concise set of 10 to 15 questions that concern handedness exclusively. One limitation of these questionnaires is that they do not address social forces that may have influenced left-handedness. The only way to guarantee validity is to combine standardized questionnaires, behavioral tests, and interviews regarding social influences.