Instance-based learning techniques typically handle continuous and linear input values well,
but often do not handle nominal input attributes appropriately. The Value Difference Metric
(VDM) was designed to find reasonable distance values between nominal attribute values, but it
largely ignores continuous attributes, requiring discretization to map continuous values into
nominal values. This paper proposes three new heterogeneous distance functions, called the
Heterogeneous Value Difference Metric (HVDM), the Interpolated Value Difference Metric
(IVDM), and the Windowed Value Difference Metric (WVDM). These new distance functions
are designed to handle applications with nominal attributes, continuous attributes, or both. In
experiments on 48 applications the new distance metrics achieve higher classification accuracy
on average than three previous distance functions on those datasets that have both nominal and
continuous attributes.