Reliability and Validity
“Instruments” are devices used to collect and measure the data.

2 important criteria for instruments:
Reliability 
An instrument is reliable if it consistently give the same results
Can be tested by
  • Test-retest
  • Equivalent form
  • Split-half


Validity
An instrument measures what it is intended to measure, and that it measures this correctly
Can be tested by

  • Criterion-referenced validity (does it accurately predict or diagnose?)
  • Construct validity (compare new instrument with old one of known validity)
  • Content validity (gather expert opinion on the questions)