On Doctoring MEDLINE searches, with reference librarian comments

The question was

"What factors are involved in chronic allograft rejection? "

1 :  Graft rejection/cl [Classification]         {76}
2 :  limit 1 to yr=1977-1999         {76}
3 :  1 or 2         {76}
4 :  from 3 keep 19,21,38         {3}
5 :  *Graft rejection/pc [Prevention & Control]         {1054}
6 :  1         {76}
7 :  *Graft Rejection/cl [Classification]         {28}
8 :  from 6 keep 3,21,65         {3}
9 :  "CHRONIC GRAFT REJECTION".mp.         {49}
10 :  from 9 keep 3-6,10-11,17-18,23,25,28,35         {12}
11 :  from 10 keep 3-4,6-9,12         {7}
12 :  from 11 keep 1-7         {7}
13 :  from 11 keep 1-7          {7}

Reference Librarian comments

Always "explode" the MeSH term. Also, I don't think I'd use that
"classification" sub-heading in set #1. (Easy for me to say, having
the time to analyze all this..)

But, congrats on your MEDLINE experience, etc. I did the search,
using a slightly different approach. (I like to keep the "limits"
till the very end. And I used all the subheadings (not
"classification" or "prevention and control," etc.) because you said:
"what are the factors..." So I figure there are probably plenty of
factors and I don't want to shrink my retrieval until I know the real
potential size. So here's what I did...

1 : 
exp *graft rejection/
6368

2 : 
exp *transplantation, homologous/
917

3 : 
1 and 2
187

4 : 
limit 3 to (human and english language)
56