A team of researchers has developed a device that can detect the presence of bacteria in gums. In the development process, they asked another team of researchers to use the device to investigate whether the external team got similar results. What was being investigated: validity or reliability of the measurements? Explain your answer.

The developed device is not expensive; it is very affordable. Both the sensitivity and specificity of the device are relatively high being more than 90%. The positive predictive value of the device is 59%. In your opinion, is this device economical? Explain your answer.