In my history courses in school, the instructors drew a sharp distinction between primary sources and secondary sources. Primary sources would date from the time of the event (or shortly thereafter), and ideally be recorded by somebody who actually witnessed the event. Secondary sources would be pretty much everything else. A secondary source might draw on primary sources, but never actually becomes one, however accurate and carefully researched it is.
When it comes to genealogy, primary sources would be things like birth certificates, census records, military records, marriage certificates, death certificates, and so on.
The measure I use in the One Name Studies that I manage is derived from Paul Gierszewski's WikiTree Statistics page. On his page, Paul's system is outlined thus:
Profiles are randomly sampled and assigned to the following categories:
- 3 or more sources, where sources are likely original records or books.
- 1 or 2 sources
- Poorly sourced, such as a link to an Ancestry tree or another website, or vague source description
- Unsourced
- Unavailable for analysis (Unlisted, Red or Orange privacy)
For the sake of deriving an average score, I have put numerical values on Paul's system, thus:
3 = 3 or more primary sources, possibly plus secondary sources
2 = 2 primary sources, possibly plus secondary sources
1 = 1 primary source, possibly plus secondary sources
0.5 = One or more secondary sources, no primary sources
0 = Unsourced or unavailable for analysis due to privacy settings
I have set up my spreadsheets to give me a "sourcing sum", which is the total number of source level values for each data set. Then I add add up the sourcing sums from all the data sets I'm using, and divide it by the number of WikiTree profiles in those same data sets to give a picture of how well (or poorly) sourced the profiles in each study are.
Notes:
- In my system, a "primary" source is a birth, baptism, census, marriage, military, death, or burial record. A "secondary" source is an entry in Wikipedia or some other encyclopedia, ThePeerage.com, an online family tree, or a book or article which covers (or at least mentions) that person.
- I don't use scores like 1.5, 2.5, etc. The 0.5 score is only to show that there is something in that profile which is "better than nothing", like an entry in ThePeerage, Wikipedia, or some family tree online somewhere.)