The reason for conducting research is to search for knowledge so that we can answer the research problem. This therefore needs that data collected must be of high quality so that we can get quality solutions. Therefore, the instruments used to measure the variables must have certain characteristics. The first characteristic is validity and the other one is reliability. These two characteristics evaluates the quality of research instruments. If the instruments are of good quality, then data collected will also be of good quality.
Validity refers to accuracy in measuring the intended construct. There are three common types of validity: content, construct and criterion-empirical.
Content validity refers to the extent to which a measuring instrument has the content of the variables and the indicators. There are two types of content validity: face and sampling validity.