Ninety-nine pregnant women, with dystocia (diffi cult childbirth or labour), were allocated at random to receive immersion in water in a birth pool

(Intervention group: Labour in water 49 women) or standard augmentation for dystocia (Control group: Augmentation 50 women) in a randomised controlled trial to evaluate the impact of labouring in water during the fi rst stage of labour (Cluett et al, 2004). The main outcome was use of epidural analgesia at any stage of labour. The results are shown in Table 2.8.
Table 2.8 Epidural analgesia data from a randomised controlled trial of labouring in water compared with standard augmentation for management of dystocia in fi rst stage of labour (Cluett et al, 2004)
Epidural analgesia at Intervention Control any stage of labour (Labour in water) (Augmentation)
Yes 23 33 No 26 17 Total 49 50 2.4 EXERCISES 25 (i) What is the proportion of women that had an epidural in each of the two groups?
(ii) What is the relative risk of the use of an epidural for the Labour in water women compared with the Augmentation women?
(iii) Calculate the OR of epidural for the Labour in water women compared with Augmentation women. Compare this estimated OR with the RR estimate from part ii: what do you notice?
(iv) Find the absolute risk difference for the use of an epidural for Labour in water compared to Augmentation.