Question

Validity, bias, reliability.

Give your own example of a measurement process that is valid but has large bias.

Also, give your own example of a measurement process that is invalid but highly reliable.

Answer 1

Validity refers to the extent that the instrument measures what it is designed to measure.

Reliability refers to the extent that the instrument yields the same results over multiple trials.

Bias refers to the tendency of a measurement process to over - estimate or under - estimate the value of a population parameter.

(i)

Example of a measurement process that is valid but has large bias:

Consider an educational test which requires fluency in English language to answer the questions. The measurement process of the educational test is valid because the objective of the assessment of the student is aptly measured by the test. But, the measurement process has large bias because the scores of the students who are not proficient in English language will under estimate the actual scores of students.

(ii)

Example of a measurement process that is invalid but highly reliable.

Consider a weighing machine with incorrect setting. So, the weighing machine is invalid because it will not give the correct weight due to incorrect setting. But, it will give the same weight of the item every time it is weighed and so in this respect it is highly reliable.