1William Molnar

Distinguish the concept “reliability” from the concept “validity,” using your own words or examples. (Please use these terms in their research sense, not their everyday meaning.  That is, not personal reliability, but statistical reliability, and validity not in the sense of a valid password or a logically valid argument, but as explained in the Trochim textbook.)

Reliability concerns the extent to which any measuring procedure yields the same results on repeated trials. The more consistent the results achieved by the same participants in the same repeated measurements, the higher the reliability of the measuring procedure; conversely the less consistent the results, the lower the reliability An assessment instrument, for example, is quite reliable if an individual obtains approximately the same score or outcome on repeated examinations. Reliability is an important indicator of an instrument’s readability, understandability, and general usefulness

Validity on the other hand is in a general sense, any measuring device that is valid if it does what it is intended to do. More specifically, validty concerns the crucial relationship between concept and indicator. Unlike reliability that focuses on the performance of empirical measures,validity is usually more of a theoretically-oriented issue because it raises the question, “valid for what purpose?” Validity is crucial to an instrument’s credibility; it is an indication that the instrument is indeed measuring what it was designed to measure and that it is measuring it accurately. Validity, like reliability, is a matter of degree. Attaining a perfectly valid indicator—one that represents the intended, and only the intended, concept—is unachievable. However, the higher an instrument’s validity the higher the likelihood that it is measuring the theoretical constructs for which it is expressly designed.

2. Provide an example of either weak reliability or weak validity.

Here is an example of a weak validity. Many recreational activities of high school students involve driving cars. A researcher, wanting to measure whether recreational activities have a negative effect on grade point average in high school students, might conduct a survey asking how many students drive to school and then attempt to find a correlation between these two factors. Because many students might use their cars for purposes other than or in addition to recreation (e.g., driving to work after school, driving to school rather than walking or taking a bus), this research study might prove invalid. Even if a strong correlation was found between driving and grade point average, driving to school in and of itself would seem to be an invalid measure of recreational activity.

2William Molnar

3. Describe the relationship between reliability and validity

When using reliability and validity, the following four results can occur:

1) High reliability, but low validity — the indicators measure something consistently but not the intended concept;

2) High validity, but low reliability — the indicator represents the concept well but does not produce consistent measurements;

3) Low validity and low reliability — the worst case; the indicators neither measure the concept nor produce consistent results of whatever they measure; or

4) High validity and high reliability — what we hope for; the indicators consistently measure what they were intended to measure.

When poor validity or reliability results occur, a researcher has to seek the source of error, revise the measuring instrument as appropriate, and test again for validity and reliability.