Table 1

Results of regression analysis to detect an association between smokefree legislation in England and emergency hospital admissions for asthma

Effects*edf†Parameter estimateStandard errorp value‡
Parametric terms
 North East§
 North West0.0500.0220.02
 Yorkshire and Humber0.0350.0230.13
 East Midlands−0.120.024<0.001
 West Midlands0.0510.0230.02
 East of England−0.280.024<0.001
 South East−0.310.023<0.001
 South West−0.220.024<0.001
Smooth terms
 North East1.000.008
 North West6.17<0.001
 Yorkshire and Humber2.280.21
 East Midlands2.790.06
 West Midlands2.820.32
 East of England1.000.03
 South East3.67<0.001
 South West4.30<0.001
  • *AR(1) term=0.22.

  • †edf, the effective degrees of freedom for the smooth term is a measure of the complexity of the estimated smooth term. For example, the edf for each region in the Region×Year effect represents the degree of non-linearity of the long-term trend in that region. If edf=1, the shape of the relationship between the smooth term and the outcome is linear. Values of edf increase progressively with the addition of more non-linear relationships.

  • ‡p value from a t test on parametric regression coefficients and F test on smooth terms. p Values for smooth terms test the null hypothesis that there is no relationship between the smooth term and emergency admissions for asthma.

  • §Baseline category.