Bayesian approach for sample size determination, illustrated with Soil Health Card data of Andhra Pradesh (India).

A crucial decision in designing a spatial sample for soil survey is the number of sampling locations required to answer, with sufficient accuracy and precision, the questions posed by decision makers at different levels of geographic aggregation. In the Indian Soil Health Card (SHC) scheme, many thousands of locations are sampled per district. In this paper the SHC data are used to estimate the mean of a soil property within a defined study area, e.g., a district, or the areal fraction of the study area where some condition is satisfied, e.g., exceedence of a critical level. The central question is whether this large sample size is needed for this aim. The sample size required for a given maximum length of a confidence interval can be computed with formulas from classical sampling theory, using a prior estimate of the variance of the property of interest within the study area. Similarly, for the areal fraction a prior estimate of this fraction is required. In practice we are uncertain about these prior estimates, and our uncertainty is not accounted for in classical sample size determination (SSD). This deficiency can be overcome with a Bayesian approach, in which the prior estimate of the variance or areal fraction is replaced by a prior distribution. Once new data from the sample are available, this prior distribution is updated to a posterior distribution using Bayes' rule. The apparent problem with a Bayesian approach prior to a sampling campaign is that the data are not yet available. This dilemma can be solved by computing, for a given sample size, the predictive distribution of the data, given a prior distribution on the population and design parameter. Thus we do not have a single vector with data values, but a finite or infinite set of possible data vectors. As a consequence, we have as many posterior distribution functions as we have data vectors. This leads to a probability distribution of lengths or coverages of Bayesian credible intervals, from which various criteria for SSD can be derived. Besides the fully Bayesian approach, a mixed Bayesian-likelihood approach for SSD is available. This is of interest when, after the data have been collected, we prefer to estimate the mean from these data only, using the frequentist approach, ignoring the prior distribution. The fully Bayesian and mixed Bayesian-likelihood approach are illustrated for estimating the mean of log-transformed Zn and the areal fraction with Zn-deficiency, defined as Zn concentration <0.9 mg kg -1, in the thirteen districts of Andhra Pradesh state. The SHC data from 2015-2017 are used to derive prior distributions. For all districts the Bayesian and mixed Bayesian-likelihood sample sizes are much smaller than the current sample sizes. The hyperparameters of the prior distributions have a strong effect on the sample sizes. We discuss methods to deal with this. Even at the mandal (sub-district) level the sample size can almost always be reduced substantially. Clearly SHC over-sampled, and here we show how to reduce the effort while still providing information required for decision-making. R scripts for SSD are provided as supplementary material.

Conservative treatment versus elective repair of umbilical hernia in patients with liver cirrhosis and ascites: results of a randomized controlled trial (CRUCIAL trial).

PURPOSE: To establish optimal management of patients with an umbilical hernia complicated by liver cirrhosis and ascites. METHODS: Patients with an umbilical hernia and liver cirrhosis and ascites were randomly assigned to receive either elective repair or conservative treatment. The primary endpoint was overall morbidity related to the umbilical hernia or its treatment after 24 months of follow-up. Secondary endpoints included the severity of these hernia-related complications, quality of life, and cumulative hernia recurrence rate. RESULTS: Thirty-four patients were included in the study. Sixteen patients were randomly assigned to elective repair and 18 to conservative treatment. After 24 months, 8 patients (50%) assigned to elective repair compared to 14 patients (77.8%) assigned to conservative treatment had a complication related to the umbilical hernia or its repair. A recurrent hernia was reported in 16.7% of patients who underwent repair. For the secondary endpoint, quality of life through the physical (PCS) and mental component score (MCS) showed no significant differences between groups at 12 months of follow-up (mean difference PCS 11.95, 95% CI - 0.87 to 24.77; MCS 10.04, 95% CI - 2.78 to 22.86). CONCLUSION: This trial could not show a relevant difference in overall morbidity after 24 months of follow-up in favor of elective umbilical hernia repair, because of the limited number of patients included. However, elective repair of umbilical hernia in patients with liver cirrhosis and ascites appears feasible, nudging its implementation into daily practice further, particularly for patients experiencing complaints. TRIAL REGISTRATION: Clinicaltrials.gov , NCT01421550, on 23 August 2011.

Meta-analysis of glue versus sutured mesh fixation for Lichtenstein inguinal hernia repair.

BACKGROUND: Chronic pain remains a frequent complication after Lichtenstein inguinal hernia repair. As a consequence, mesh fixation using glue instead of sutures has become popular. This meta-analysis aimed to clarify which fixation technique is to be preferred for elective Lichtenstein inguinal hernia repair. METHODS: A meta-analysis was conducted according to the PRISMA guidelines. Articles published between January 1990 and April 2012 were searched for in MEDLINE, Embase and the Cochrane Library. Randomized controlled trials (RCTs) comparing glue and sutured mesh fixation in elective Lichtenstein repair for unilateral inguinal hernia were included. The quality of the RCTs and the potential risk of bias were assessed using the Cochrane risk of bias tool. RESULTS: Of 254 papers found in the initial search, a meta-analysis was conducted of seven RCTs comprising 1185 patients. With the use of glue mesh fixation, the duration of operation was shorter (mean difference -2·57 (95 per cent confidence interval (c.i.) -4·88 to -0·26) min; P = 0·03), patients had lower visual analogue scores for postoperative pain (mean difference -0·75 (-1·18 to -0·33); P = 0·001), early chronic pain occurred less often (risk ratio 0·52, 95 per cent c.i. 0·31 to 0·87; P = 0·01), and time to return to daily activities was shorter (mean difference -1·17 (-2·30 to -0·03) days; P = 0·04). The hernia recurrence rate did not differ significantly. CONCLUSION: Elective Lichtenstein repair for inguinal hernia using glue mesh fixation compared with sutures is faster and less painful, with comparable hernia recurrence rates.

Meta-analysis of laparoscopic versus open cholecystectomy for patients with liver cirrhosis and symptomatic cholecystolithiasis.

BACKGROUND: Open cholecystectomy (OC) is often preferred over laparoscopic cholecystectomy (LC) in patients with liver cirrhosis and portal hypertension, but evidence is lacking to support this practice. This meta-analysis aimed to clarify which surgical technique is preferable for symptomatic cholecystolithiasis in patients with liver cirrhosis. METHODS: A meta-analysis was conducted according to the PRISMA guidelines. Articles published between January 1990 and October 2011 were identified from MEDLINE, Embase and the Cochrane Library. Randomized clinical trials (RCTs) comparing outcomes of OC versus LC for cholecystolithiasis in patients with liver cirrhosis were included. The quality of the RCTs was assessed using the Jadad criteria. RESULTS: Following review of 1422 papers by title and abstract, a meta-analysis was conducted of four RCTs comprising 234 surgical patients. They provided evidence of at least level 2b on the Oxford Level of Evidence Scale, but scored poorly according to the Jadad criteria. Some 97·0 per cent of the patients had Child-Turcotte-Pugh (CTP) grade A or B liver cirrhosis. In all, 96·6 per cent underwent elective surgery. No postoperative deaths were reported. LC was associated with fewer postoperative complications (risk ratio 0·52, 95 per cent confidence interval (c.i.) 0·29 to 0·92; P = 0·03), a shorter hospital stay (mean difference -3·05 (95 per cent c.i. -4·09 to -2·01) days; P < 0·001) and quicker resumption of a normal diet (mean difference -27·48 (-30·96 to -23·99) h; P < 0·001). CONCLUSION: Patients with CTP grade A or B liver cirrhosis who undergo LC for symptomatic cholecystolithiasis have fewer overall postoperative complications, a shorter hospital stay and resume a normal diet more quickly than those who undergo OC.

Cost-effectiveness of screening for abdominal aortic aneurysm in the Netherlands and Norway.

BACKGROUND: The aim of this study was to determine the cost-effectiveness of ultrasound screening for abdominal aortic aneurysm (AAA) in men aged 65 years, for both the Netherlands and Norway. METHODS: A Markov model was developed to simulate life expectancy, quality-adjusted life-years, net health benefits, lifetime costs and incremental cost-effectiveness ratios for both screening and no screening for AAA. The best available evidence was retrieved from the literature and combined with primary data from the two countries separately, and analysed from a national perspective. A threshold willingness-to-pay (WTP) of €20,000 and €62,500 was used for data from the Netherlands and Norway respectively. RESULTS: The additional costs of the screening strategy compared with no screening were €421 (95 per cent confidence interval 33 to 806) per person in the Netherlands, and the additional life-years were 0·097 (-0·180 to 0·365), representing €4340 per life-year. For Norway, the values were €562 (59 to 1078), 0·057 (-0·135 to 0·253) life-years and €9860 per life-year respectively. In Norway the results were sensitive to a decrease in the prevalence of AAA in 65-year-old men to 1 per cent, or lower. Probabilistic sensitivity analyses indicated that AAA screening has a 70 per cent probability of being cost-effective in the Netherlands with a WTP threshold of €20,000, and 70 per cent in Norway with a threshold of €62,500. CONCLUSION: Using this model, screening for AAA in 65-year-old men would be highly cost-effective in both the Netherlands and Norway.

Emergency repair of inguinal hernia in the premature infant is associated with high direct medical costs.

PURPOSE: Inguinal hernia repair is frequently performed in premature infants. Evidence on optimal management and timing of repair, as well as related medical costs is still lacking. The objective of this study was to determine the direct medical costs of inguinal hernia, distinguishing between premature infants who had to undergo an emergency procedure and those who underwent elective inguinal hernia repair. METHODS: This cohort study based on medical records concerned premature infants with inguinal hernia who underwent surgical repair within 3 months after birth in a tertiary academic children's hospital between January 2010 and December 2013. Two groups were distinguished: patients with incarcerated inguinal hernia requiring emergency repair and patients who underwent elective repair. Real medical costs were calculated by multiplying the volumes of healthcare use with corresponding unit prices. Nonparametric bootstrap techniques were used to derive a 95 % confidence interval (CI) for the difference in mean costs. RESULTS: A total of 132 premature infants were included in the analysis. Emergency surgery was performed in 29 %. Costs of hospitalization comprised 65 % of all costs. The total direct medical costs amounted to €7418 per premature infant in the emergency repair group versus €4693 in the elective repair group. Multivariate analysis showed a difference in costs of €1183 (95 % CI -1196; 3044) in favor of elective repair after correction for potential risk factors. CONCLUSION: Emergency repair of inguinal hernia in premature infants is more expensive than elective repair, even after correction for multiple confounders. This deserves to be taken into account in the debate on timing of inguinal hernia repair in premature infants.

Umbilical hernia management during liver transplantation.

PURPOSE: Patients with liver cirrhosis scheduled for liver transplantation often present with a concurrent umbilical hernia. Optimal management of these patients is not clear. The objective of this study was to compare the outcomes of patients who underwent umbilical hernia correction during liver transplantation through a separate infra-umbilical incision with those who underwent correction through the same incision used to perform the liver transplantation. METHODS: In the period between 1990 and 2011, all 27 patients with umbilical hernia and liver cirrhosis who underwent hernia correction during liver transplantation were identified in our hospital database. In 17 cases, umbilical hernia repair was performed through a separate infra-umbilical incision (separate incision group) and 10 were corrected from within the abdominal cavity without a separate incision (same incision group). Six patients died during follow-up; no deaths were attributable to intraoperative umbilical hernia repair. All 21 patients who were alive visited the outpatient clinic to detect recurrent umbilical hernia. RESULTS: One recurrent umbilical hernia was diagnosed in the separate incision group (6 %) and four (40 %) in the same incision group (p = 0.047). Two patients in the same incision group required repair of the recurrent umbilical hernia; one of whom underwent emergency surgery for bowel incarceration. The one recurrent hernia in the separate incision group was corrected electively. CONCLUSION: In the event of liver transplantation, umbilical hernia repair through a separate infra-umbilical incision is preferred over correction through the same incision used to perform the transplantation.

Sense and nonsense of influenza vaccination in asthma and chronic obstructive pulmonary disease.

Although influenza is generally seen as an important cause of excess mortality in patients with asthma or chronic obstructive pulmonary disease (COPD), this mortality is nearly exclusively present in patients over the age of 60. Morbidity in patients with asthma or COPD is related to respiratory infections, including influenza. Vaccination against influenza has proven to be effective in nursing home populations, decreasing both mortality and morbidity during epidemics of influenza A. In younger patients with asthma or COPD, however, the effect of vaccination is more ambiguous. Exacerbation of respiratory disease is not due to influenza vaccination (except in allergy to chicken protein), from which we can conclude that influenza vaccination is a safe method to prevent a potentially serious respiratory infection in patients with asthma or COPD.