IGI is the International Genealogical Index. It is owned by the LDS Church and can be foound free on the net at www.familysearch.org
It has extracted records from Parish Registers (source numbers begining C,M, P ) but also data supplied by LDS patrons as a result of their researches, which may not be quite so accurate. There is a lot of data for Scotland up to about 1875.
It must however be remembered that IGI is an Index - and not a complete one - just because there is no entry for a person or event it doesn't mean that it didn't happen. Also the real registers may have more information than on an index - abodes, occupations, ages, etc.
Once an entry has been found on IGi every effort should be made to look at the 'real' record to see what it contains.
Fiona (board admin)