问题如下:
A database of hedge fund returns is constructed as follows. The first year of the database is 1994. All funds existing as of the end of 1994 that a willing to report their verified returns for that year are included in that year. The database is extended by asking the funds for verified returns before 1994. Subsequently, funds are added as they are willing to report verified returns to the database. If a fund stops reporting returns, its returns are deleted from the database, but the database has an agreement with funds that they will keep reporting verified returns even if they stop being open to new investors. Which of the following four statements are correct?
I. The database suffers from backfilling bias.
II. The database suffers from survivorship bias.
III. The database suffers from an errors-in-variables bias.
IV. The equally weighted annual return average of fund returns will under-estimate the performance one would expect from a hedge fund.
选项:
A.All the above statements are correct.
B.Statements I and II are correct.
C.Statements I, II, and III are correct.
D.Statements II and IV are correct.
解释:
B is correct. The database includes histories before 1994 and therefore suffers from backfill bias. Next, funds that stop reporting are deleted from the database, so it has survivorship bias. Errors-in-variables bias arises in other contexts, such as regression. Finally, the average of fund returns will be too high (not too low) because of these two biases. Hence, I. and II. are correct.
I 中的backfilling bias怎么理解?为什么包括了1994年以前的数据,就有backfilling bias了?