What are the characteristics of a good measurement tool? An intuitive answer to this question is that the tool should be an accurate counter or indicator of what we are interested in measuring.
In addition, it should be easy and efficient to use. There are three (3) major criteria for evaluating a measurement tool:
- Validity: This refers to the extent to which a test measures what we actually wish to measure.
- Reliability: has to do with the accuracy and precision of a measurement procedure.
- Practicality: is concerned with a wide range of factors of economy, convenience, and interpretability.
Validity in research
Validity in research is achieved through the internal and external validity of the study.
Internal validity: This refers to the outcome of the study as based on the function of the program, a study has internal validity if the outcome of the study is a function of the approach being tested rather than results of the causes not systematically dealt with.
Internal validity is justified by the conclusions we have as researchers when we have been able to control the threats of other variables (i.e intervening variables, or moderating variables or extraneous variables). The more you reduce the nuisances (other variables) affecting the study, the more you attain the internal validity. There are three widely accepted classification of internal validity:
- content validity
- criterion – related validity
- construct validity
1. Content validity
The content validity of a measuring instrument is the extent to which it provides adequate coverage of the topic under study. If the instrument contains a representative sample of the universe of subject matter of interest, then content validity is good. To evaluate the content validity of an instrument, one must first agree on what elements constitute adequate coverage of the problem.
Criterion-related validity reflects the success of measures used for prediction or estimation. You may want to predict an outcome or estimate the existence of a current behaviour or condition. These are predictive and concurrent validity, respectively. They differ only in a time perspective. An opinion questionnaire that correctly forecasts the outcome of a union election has predictive validity. An observational method that correctly categorizes families by current income class has concurrent validity. While these examples appear to have simple and ambiguous validity criteria, there are difficulties in estimating validity. Consider the problem of estimating family income. There clearly is a knowable true income for every family. However, we may find it difficult to secure this figure. Thus, while the criterion is conceptually clear, it may be unavailable.
One may also wish to measure or infer the presence of abstract characteristics for which no empirical validation seems possible. Attitude scales and aptitude and personality tests generally concern concepts that fall in this category. Although this situation is much more difficult, some assurance is still needed that the measurement has an acceptable degree of validity. In attempting to evaluate construct validity, we consider both the theory and the measuring instrument being used. If we were interested in measuring the effect of ceremony on organizational culture, the way in which ceremony was operationally defined would have to correspond to an empirically grounded theory. Once assured that the construct was meaningful in a theoretical sense, we would next investigate the adequacy of the instrument. If a known measure of ceremony in organizational culture was available, we might correlate the results
obtained using this measure with those derived from our new instrument. Such an approach would provide us with preliminary indications of convergent validity.
Reliability means many things to many people, but in most contexts the notion of consistency emerges. A measure is reliable to the degree that it supplies consistent results. Reliability is a contributor to validity and is a necessary but not sufficient condition for validity. The relationship between reliability and validity can be simply illustrated with the use of a bathroom scale. If the scale measures your weight correctly (using a concurrent criterion such as a scale known to be accurate), then it is both reliable and valid. If it consistently overweighs you by six pounds, then the scale is reliable but not valid. If the scale measures erratically from time to
time, then it is not reliable and therefore cannot be valid.
Reliability is concerned with estimates of the degree to which a measurement is free of random or unstable error. It is not as valuable as validity determination, but it is much easier to assess. Reliable instruments can be used with confidence that transient and situational factors are not interfering. Reliable instruments are robust; they work well at different times under different conditions.