This might mean, for example, that an otherwise significant difference between two values may not be detected by a statistical test due to the increased variance of data resulting from unreliable instruments only (O’Dwyer & Bernauer, 2014). If an instrument is unreliable, it means that it will give non-precise results of measurements. The reliability of an instrument is also paramount for the credibility of a study and the value of the evidence. High validity means that the instrument measured what it was supposed to measure, which is a necessary condition for the credibility of a study, whereas evidence gained via non-valid instrument may simply be misleading (Cozby & Bates, 2015). The validity of an instrument has a crucial impact on the credibility of a study and the value of the evidence. How does the validity and reliability of an instrument influence the credibility of the study and the value of the evidence? If a tool is reliable, then it measures the magnitude in the question precisely but if it is highly unreliable, the measurement will be very inaccurate, which also makes the results not adequate. The reliability of an instrument estimates whether it produces similar results if used to measure the same thing in non-changing conditions (Cozby & Bates, 2015). If an instrument is not valid, it means that its results cannot be trusted for instance, a ruler is not a valid instrument for measuring weight, so a hypothetical study measuring weight with a ruler cannot be trusted to produce adequate results (Cozby & Bates, 2015). 73) it determines whether the instrument measures what it is supposed to measure. The validity of an instrument (construct validity) assesses the accuracy of that instrument (Cozby & Bates, 2015, p.

Reliability of research instrument