Sources of data

Source and collection method is known and verified

Data can be available from different locations and time periods

Cannot be certain of accuracy of data

The exact data required can be collected

Do not know bias was placed on collection

Data being collected can change in response to answers.

May not get a large range of data

Data from different locations and time periods is available

Analysis of the data may already be complete

The collection method is known and verified.

Large range of data available