  Citation networks have fed numerous works in scientific evaluation, science
mapping (and more recently large-scale network studies) for decades. The
variety of citation behavior across scientific fields is both a research topic
in sociology of science, and a problem in scientific evaluation. Normalization,
tantamount to a particular weighting of links in the citation network, is
necessary for allowing across-field comparisons of citation scores and
interdisciplinary studies. In addition to classical normalization which
drastically reduces all variability factors altogether, two tracks of research
have emerged in the recent years. One is the revival of iterative "influence
measures". The second is the "citing-side" normalization, whose only purpose is
to control for the main factor of variability, the inequality in citing
propensity, letting other aspects play: knowledge export/imports and growth.
When all variables are defined at the same field-level, two propositions are
established: (a) the gross impact measure identifies with the product of
relative growth rate, gross balance of citation exchanges, and relative number
of references (b) the normalized impact identifies with the product of relative
growth rate and normalized balance. At the science level, the variance of
growth rate over domains is a proxy for change in the system, and the variance
of balance a measure of inter-disciplinary dependences. This opens a new
perspective, where the resulting variance of normalized impact, and a related
measure, the sum of these variances proposed as a Change-Exchange Indicator,
summarize important aspects of science structure and dynamism. Results based on
a decade's data are discussed. The behavior of normalized impact according to
scale changes is also briefly discussed.
