1. Reliability and Validity Dr. Roy Cole Department of Geography and Planning GVSU

2. Reliability Definition.  The consistency of a measure.  The extent to which a measure (or instrument) measures the same way under the same conditions with the same respondents.  A measure is reliable when a person’s score is the “same” from one time to the next. Estimating reliability.  Test-Retest method. Administer the instrument (measurements) twice at two separate times. Calculate the correlation between the two measurements.  Split-Half method. Randomly divide all question items that measure the same concept into two halves (sets). Administer the questions to the same sample of people. Calculate the correlation between the two sets of measurements.

3. Reliability  Inter-rater reliability. When two or more people observe and rate the same object. Start with a pilot study. Develop guidelines so that raters observe in the same way. For categorized observations, calculate the percent of agreement between the raters.

4. Validity Definition.  Concerns the validity of the researcher’s operationalization.  Does the purported measure really measure the concept it is supposed to measure? Types of validity.  Face validity. Does (do) the measure(s) appear to measure the concept?  Content (logical) validity. Do the measures capture all of the dimensions of the concept?  Predictive validity. Do the measures predict something that we should expect it to predict? A measure of math ability should be able to predict how well high school students will do in university mathematics.

5. Reliability and validity together