  Using the CD-ROM version of the Science Citation Index 2010 (N = 3,705
journals), we study the (combined) effects of (i) fractional counting on the
impact factor (IF) and (ii) transformation of the skewed citation distributions
into a distribution of 100 percentiles and six percentile rank classes (top-1%,
top-5%, etc.). Do these approaches lead to field-normalized impact measures for
journals? In addition to the two-year IF (IF2), we consider the five-year IF
(IF5), the respective numerators of these IFs, and the number of Total Cites,
counted both as integers and fractionally. These various indicators are tested
against the hypothesis that the classification of journals into 11 broad fields
by PatentBoard/National Science Foundation provides statistically significant
between-field effects. Using fractional counting the between-field variance is
reduced by 91.7% in the case of IF5, and by 79.2% in the case of IF2. However,
the differences in citation counts are not significantly affected by fractional
counting. These results accord with previous studies, but the longer citation
window of a fractionally counted IF5 can lead to significant improvement in the
normalization across fields.
