text: A test is valid when it measures what it is supposed to. It is reliable it yields consistent results. You find out more at:\nhttp://www.georgetown.edu/departments/psychology/researchmethods/researchanddesign/validityandreliability.htm\n\nThe disadvantages of using secondary data:\nYou do not have the control over how the instrument is designed, how they are collected, or how carefully they are manipulated and documented. Another serious trade-off between primary and secondary data is the issue of anomalies; when you are using data you have collected yourself, you have a clear understanding of how those data should appear (in a frequency table, for example). You are more quickly able to spot and correct those anomalies. If you are using someone else's data, you won't necessarily know all of the subtleties that were involved in making coding decisions and in inputting the data.\nhttp://ed.isu.edu/research/Procedures/DataType.htm