“A valid instrument is always reliable, but a reliable instrument may not always bevalid.” Comment on this statement.

This statement is highlighting the difference between two key concepts in research: reliability and validity.

1. Reliability refers to the consistency of a measure. A test is considered reliable if we get the same result repeatedly. For example, if a test is designed to measure a trait such as intelligence, then each time the test is administered to a subject, the results should be approximately the same. Hence, a reliable instrument is one that consistently gives the same results, assuming what is being measured is not changing.

2. Validity refers to how well a test measures what it is purported to measure. While a test might give very consistent results (i.e., be highly reliable), it may not necessarily be measuring what it is intended to measure. For example, a test of intelligence should measure intelligence and not something else such as memory ability.

So, when the statement says "A valid instrument is always reliable", it means that if a test accurately measures what it's supposed to measure (validity), it will naturally give consistent results (reliability).

However, the reverse, "a reliable instrument may not always be valid", is also true. Just because a test gives consistent results, doesn't mean it's measuring what it's supposed to measure. For example, a clock that is consistently 5 minutes slow is reliable (it consistently gives the same time), but it's not valid (it's not accurately measuring the current time).

In conclusion, while reliability is a necessary quality for validity, it is not sufficient on its own. A good instrument must be both reliable and valid.