OBJECTIVE
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 Outcom es SH CH R1 N o sym ptom s orcom plications 501 524 R2 N on serious com plications 6 13 R3 S erious com plications 15 20 R4 M ild sym ptoms 69 40 R5 M oderate sym ptoms 9 3 R6 S evere sym ptoms 17 6 N Totalnumberofpatients 617 606 C om plications Symptom s M ean (S E) M ean (SE) Step 1 coefficients Intercept(log scale) -3.131 (0.455) -2.801 (0.459) Treatm enteffect(log odds ratio) -0.5 (0.311) 0.876 (0.21) Betw een-study standard error 1.406 (0.49) 1.612 (0.397) Step 2 coefficients Threshold 1– notserious/serious com plication 0.622 (0.292) Threshold 2-m ild/notm ild sym ptom 1.14 (0.195) Threshold 3-notsevere/severe sym ptom -0.687 (0.3) 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 ,1..6 ,1..6 ~ ( , ) ij ij ij R Mp N 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 0 1 2 3 4 5 6 7 8 -4 -3 -2 -1 0 1 2 3 4 5 Favours SH Log-odds ratio Favours C H P rolapse 1yearormore (7 RC Ts) B leeding 1 year(6 RC Ts) S tenosis 1 year(4 R CTs) U nhealed w ounds 3 months (4 R C Ts) Incontinence 1 year(7 R C Ts) U rgency 1 year(5 R C Ts) R einterventions 1 year(12 R C Ts) Assumptions of the model
description
Figure 1: Results of a conventional meta-analysis of long-term outcomes of haemorrhoid surgery. OBJECTIVE. METHODS. Figure 2: Structure of the decision model. Mild symptoms. Symptoms. Moderate symptoms. RESULTS. Severe symptoms. Complications. Non-serious complications. - PowerPoint PPT Presentation
Transcript of OBJECTIVE
A model to calculate the absolute and relative risks of haemorrhoid surgery
David Epstein, on behalf of the University of York Technology Assessment Group
Outcomes SH CHR1 No symptoms or complications 501 524R2 Non serious complications 6 13R3 Serious complications 15 20R4 Mild symptoms 69 40R5 Moderate symptoms 9 3R6 Severe symptoms 17 6N Total number of patients 617 606
Complications Symptoms
Mean (SE) Mean (SE)
Step 1 coefficients
Intercept (log scale) -3.131 (0.455) -2.801 (0.459)
Treatment effect (log odds ratio) -0.5 (0.311) 0.876 (0.21)
Between-study standard error 1.406 (0.49) 1.612 (0.397)
Step 2 coefficients
Threshold 1– not serious/serious complication 0.622 (0.292)
Threshold 2- mild/not mild symptom 1.14 (0.195)
Threshold 3- not severe/severe symptom -0.687 (0.3)
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
,1..6 ,1..6~ ( , )ij ij ijR M p N
The overall number of patients with each outcome is shown in Table 1.
The vector of number of patients with outcomes Rij1 to Rij6 for study i and treatment j follows a multinomial distribution with a vector of probabilities pij,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
0
1
2
3
4
5
6
7
8
-4 -3 -2 -1 0 1 2 3 4 5
Favours SH Log-odds ratio Favours CH
Prolapse 1year or more (7 RCTs)
Bleeding 1 year (6 RCTs)
Stenosis 1 year (4 RCTs)
Unhealed wounds 3 months (4 RCTs)
Incontinence 1 year (7 RCTs)
Urgency 1 year (5 RCTs)
Reinterventions 1 year (12 RCTs)
Assumptions of the model
