# Selecting a Distance Function

### PCI2 currently offers 3 distance functions (D1, D2, D3)

D1

D1 is used for bipolar scales with “neutral” or “neither” responses (e.g., -3, -2, -1, 0, 1, 2, 3) and bipolar scales without “neutral” or “neither” responses (e.g., -3, -2, -1, 1, 2, 3). D1 does not include “neutral” or “neither” responses in the calculation of distance. When using D1, the distance from -2 to +1 is 2, not the algebraic difference of 3. D1 is recommended for most studies.

D2

D2 can also be used for bipolar scales with “neutral” or “neither” responses (e.g., -2, -1, 0, 1, 2). D2 includes “neutral” or “neither” responses in the calculation of distance. When using D2, the distance from -1 to +1 is 2 and the distance from -2 to +1 is 3. If circumstances associated with a given research project support believing that neutral ratings should affect distance, D2 should be used. To illustrate where D2 may be appropriate, consider an off-highway vehicle (OHV) enthusiast who staunchly believes that OHV’s should be allowed on all public lands. A wilderness purist, on the other hand, may hold equally strong beliefs in the opposite direction. If a bill was introduced into Congress that either allowed or prohibited OHV access to public lands, individuals at both ends of the spectrum might be in conflict with those who were noncommittal (i.e., neutral). The size of this neutral group could swing the vote in favor of one decision over the other.

D3

D3 is used for unipolar scales (e.g., “not at all important” to “extremely important”).