Validating a scale
Below is an example of a reliability analysis for a Recreational Shopping scale.
The analysis also elucidates the efficacy of each individual item by reporting information such as corrected item-total correlation and Cronbach’s Alpha if an item were deleted.As seen in the example below, we know that item #4 is a great item because it has a high item-total correlation (correlates strongly with the other items) and the overall reliability would drop significantly if the item were deleted from the scale.These, and other metrics all go into understanding the makings of a reliable survey.For example, let’s say a researcher gave Samantha a paper-and-pencil survey of Extraversion.How would the researcher know that the computed score on that survey actually reflected Samantha’s true level of Extraversion? Some of the most commonly assessed forms of validity include content validity, construct validity, and criterion validity.Introduction and Objectives: Measurement is an essential activity of medical science.
In order to acquire data about people, objects, and events proper data collection tools need to be designed which can measure things of scientific interest.
Content validity is an assessment of how well the breadth of the construct has been assessed.
For example, have all the elements of Extraversion been captured in the survey (e.g., gregarious, outgoing, active)?
Reliability is the degree to which an instrument consistently measures a construct -- both across items (e.g., internal consistency, split-half reliability) and time points (e.g., test-retest reliability).
One of the most common assessments of reliability is Cronbach’s Alpha, a statistical index of internal consistency that also provides an estimate of the ratio of true score to error in Classical Test Theory.
It is critical for us to recapture the psychometric properties of the original scales.