  The discussion about counting methods in bibliometrics is often reduced to
the choice between full and fractional counting. However, several studies
document that this distinction is too simple. The aim of the present study is
to give an overview of counting methods in the bibliometric literature and to
provide insight into their properties and use. A mix of methods is used. In the
preliminary results, a literature review covering 1970-2018 identified 29
original counting methods. Seventeen were introduced in the period 2010-2018.
Twenty-one of the 29 counting methods are rank-dependent and fractionalized
meaning that the authors of a publications share 1 credit but do not receive
equal shares, for example harmonic counting. The internal and external
validation of the counting methods are assessed. Three criteria for
well-constructed bibliometric indicators - adequacy, sensitivity, and
homogeneity - are used to assess the internal validity. Regarding the external
validation of the counting methods, it is investigated whether the intentions
in the studies that introduced the 29 counting methods comply with the
subsequent use of the counting methods. This study has the potential to give a
solid foundation for the use of and discussion about counting methods.
