It is an interesting issue whether DIY is a formal or informal expression.
I tried the BNC and all of the 426 instances of DIY were found in writing - none in the spoken part.
In the writtten categories, DIY is most frequent in the written-to-be-spoken category, but is also used in books and periodicals and written misc categories.
In terms of the text domains, DIY is most frequent in Leisure, and Commerce and business, followed by Applied science, and Brief and thought. with the possible exception of Leisure, all of the other domains are scientific writing.
The above evidence appears to suggest that the statement that DIY is an informal expression is ungrounded.
以下是引用 fuyanger 在 2006-5-5 22:44:37 的发言：
"a DIY corpus" seems to me not as formal as required of the language used in most research discourse. "Self-built or compiled" may suffice to make yourself clear.