The share of respondents reporting an increase minus the share reporting a decrease
A survey score where zero (or 50, depending on the convention) means as many respondents see things improving as worsening.
Business surveys ask whether activity is higher, the same or lower. A diffusion index reports the balance of answers. The regional Fed surveys centre on zero; purchasing managers' indexes centre on 50. Either way the level says how widespread a change is, not how large.