ISI Impact Factor
A=
total cites in 1992
B= 1992 cites to articles published in 1990-91 (this is a subset of A)*
B= 1992 cites to articles published in 1990-91 (this is a subset of A)*
C=
number of articles published in 1990-91
D= B/C = 1992 impact factor
D= B/C = 1992 impact factor