Q. Write a long note on choosing measures.
A. No matter what is the design of your research, your study will involve measuring the values of the variables included the design. There are many ways in which a giver variable can be measured. So, let us go through several important characteristics of a measure.
a. Assessing validity: We have already discussed the concepts of the internal and the external validity, which are attributes of research design. Here we will discuss other forms of validity that applies to measure. The validity of the measure is the extent to which it measure the thing to you want to measure. Imagine, for eg, that you decide to measure a person’s general intelligence by placing a tape measure around that person’s skull at the level of his / her forehead, on the theory that larger skulls house larger brains produce higher intelligence. In this case tape measures is a valid measure of length but actually is it a valid measure intelligence? No, because measures of skull and brain size turned out to be unrelated to intelligence and it was later found that the largest brains on record belonged to retarded person. Thus measures of intelligence based on skull or brain sizes turn out to be valid.
b. Demonstrating Reliability and Accuracy: The reliability of a measure concerns its ability to produce similar results when repeated measurements are made under identical condition. The term accuracy means a measure that produces results that agree with a known standard. A particular measuring instrument can be inaccurate but reliable, but the converse is not true. It cannot be unreliable but true. For eg; a thermometer whose glass has slipped down in its bracket may read 21% each time it is immersed in water under ice water. But as it gives same reading every time in the same conditions, it is reliable. If the thermometer reading does not agree with a known standard, as it is reliable, it cannot be accurate.