CREATE TABLE table_name_22 (year INTEGER, result VARCHAR, extra VARCHAR, tournament VARCHAR, venue VARCHAR)
What is the average year that anna thompson had an 8th place result in team competition at the world cross country championships in st etienne, france with
SELECT AVG(year) FROM table_name_22 WHERE tournament = "world cross country championships" AND venue = "st etienne, france" AND extra = "team competition" AND result = "8th"