116 Carl F. Ihler et al. treated cases and heart rate and abnormal mu- cous membranes as signiﬁcant predictors in surgically treated cases (Table 4). In the simu- lated "ﬁeld" situation the ﬁnal model also in- cluded heart rate and abnormal mucous mem- branes (Table 4). The prediction curves for the 2 treatment groups are presented in Fig. 1, while the ROC curves and sensitivity and speci- ﬁcity curves are illustrated in Fig. 2.The ROC curve described an area under curve of 87% for medical cases and 94% for surgical cases. No inﬂuential outliers were found in the regres- sion diagnostics. Grouping the continuous vari- ables into quartiles gave no better model ﬁt than analysing the variables as continuous ones. Supplementary tests also indicated (kernel smoothing) linearity of the continuous vari- ables. Discussion Material and methods As all horses in the present study are referred cases as non-responders to initial treatment(s) in the general practice, they represent a selected material compared to colic cases in general. That means that neither colic cases with their origin in simple spastic intestines and mild ob- structions nor severe colic cases, in which the pain was not possible to reduce to an acceptable level before transportation to the hospital, are represented in the study. The exclusion of cases that required surgery but were euthanised of economical or other reasons was necessary to ensure that all horses were eu- thanised at the terminal stage of the disease. However, it may be difﬁcult to classify a patient to be at the terminal stage. To avoid unneces- sary suffering when all possible further treat- ment was performed was very important when classifying non-survival. The study was performed over 2 periods of time (1997 and 1999). Year of inclusion might have inﬂuenced the results. The same protocol for Acta vet. scand. vol. 45 no. 1-2, 2004 clinical and laboratory examination throughout the study was used to avoid such bias. In the sta- tistical analysis no association between year of inclusion and survival was detected. Results The survival percentage of 63 for all colic cases in the present study is on the same level as re- ported from other studies on hospitalised colic cases (Ebert 1994, Sandholm et al. 1995). The probabilities of survival in surgically and med- ically colic cases (48 and 78%, respectively) also correspond to previous studies (Sandholm et al. 1995, Siebke 1995). In the present study there was no association between age and gender and outcome while some studies have reported that older horses have a higher risk of non-survival (Orsini et al. 1988, Reeves et al. 1989). In line with the pre- sent study, Reeves et al. (1990) and Thoefner et al. (2000) reported no association between age and the outcome in colic cases. Thoefner et al. (2000) reported an increased risk of death in cold-blooded ponies compared to a heterogeneous group of warm-blooded horses. In the present study no association be- tween breed and survival was found. In agree- ment with Thoefner et al. (2000) and Reeves et al. (1990) no association between gender and outcome was found. The degree of pain (pain score 1-3) at the initial examination in the hospital did not show any association with the outcome of the colic cases. This is in disagreement with Thoefner et al. (2000), Puotonen-Reinert (1986) and Reeves et al. (1990). In the present study most horses were given analgesics and/or NSAID before and for some horses during the transportation. When given NSAIDs and analgesics at differ- ent times before the clinical evaluation the ini- tial pain at arrival might not give the correct picture of the real clinical situation and further might explain why pain did not inﬂuence the