1. A model to calculate the absolute and relative risks of haemorrhoid surgery David Epstein, on behalf of the University of York Technology Assessment Group OBJECTIVE Adverse outcomes –complications of surgery or return of symptoms - were reported in many ways: e.g. prolapse, bleeding, incontinence or re- interventions. Meta-analyses of each outcome separately (Figure 1) do not take into account: that the outcomes are not mutually exclusive (e.g. patients may report either prolapse or bleeding or both) that the type of re-intervention undertaken offers information about the underlying severity of the symptom or complication To construct a statistical model to calculate The probabilities of symptoms and complications for CH surgery The relative risks of symptoms and complications for the SH procedure Long-term results of surgery reported in RCTs were classified into 6 mutually exclusive outcomes using a decision model structure (Figure 2): Mild, moderate and severe symptoms Non-serious and serious complications No symptom or complication METHODS RESULTS CONCLUSIONS BACKGROUND THE STATISTICAL MODEL The overall number of patients with each outcome is shown in Table 1. The vector of number of patients with outcomes R ij 1 to R ij 6 for study i and treatment j follows a multinomial distribution with a vector of probabilities p ij,1..6 The probabilities of each of the outcomes R1 to R6 were calculated in a two-step model. The first step calculated the probability of observing no symptom or complication, a complication, or a symptom, assuming the errors followed a logistic distribution, with random study effects for the intercepts and treatment effects each for complications and symptoms in the linear predictors. The second step calculated the probabilities that a symptom was mild, moderate or severe using a ordered logit (threshold) model, that is, assuming severity is the expression of a latent variable. The probability that a complication was serious was calculated using a binary logit model. Table 1: The overall number of patients with each outcome, from 16 RCTs This study has calculated the probabilities of symptoms and complications after SH and CH. There were significantly more patients with symptoms following SH; OR = exp(0.88) = 2.4 (95%CI 1.6 to 3.6) There were no significant differences between CH and SH in the number of long term complications; OR = 0.61 (95%CI 0.33 to 1.12) The full report is available on the NICE website www.nice.org.uk Serious complications No symptoms or complications Non-serious complications Mild symptoms Moderate symptoms Severe symptoms Symptoms Complications Figure 2: Structure of the decision model NICE recently evaluated two surgical procedures for the treatment of haemorrhoids: a stapled procedure (SH) versus conventional surgery (CH). Symptoms (e.g bleeding, prolapse) occur independently Symptoms with no re-intervention are mild Symptoms with an outpatient or non-excisional re-intervention are moderate Symptoms with a surgical re-intervention are severe Complications (which are relatively rare) are mutually exclusive Unhealed wounds, urgency and incontinence are serious complications Mild, moderate and severe symptoms express an underlying (latent) scale of severity Table 2: The coefficients and standard errors of the statistical model Table 2 shows the results of the statistical model, calculated using WinBUGS software using Markov Chain Monte Carlo simulation. Figure 1: Results of a conventional meta-analysis of long-term outcomes of haemorrhoid surgery Assumptions of the model