Variables of equation 3, estimating the probability for a male or a female infant of needing treatment for IHPS
| β, male | SE | p value | β, female | SE | p value | |
| β0, constant | +3.52717 | 0.76298 | −0.61042 | 1.527605 | ||
| Y, days after 31 Dec 1986 | −0.00015 | 0.00002 | <0.0001 | −0.00007 | 0.00005 | 0.1665 |
| Z, latitude, degrees | −0.15599 | 0.01322 | <0.0001 | −0.10999 | 0.02639 | <0.0001 |
| U, urbanisation, rated 1–9 | +0.02076 | 0.01191 | 0.0814 | −0.01816 | 0.02457 | 0.4598 |
| V, geographical location, rated 1–3 | −0.01202 | 0.03697 | 0.7451 | +0.04351 | 0.07163 | 0.5600 |
The value of a β coefficient indicates the degree and direction of the effect of its variable in the function. Urbanisation was rated from 1 to 9, with low values for urban areas. Geographical location was rated from 1 to 3, with 1 for coast and 3 for inland areas.