Two-stage Group Research Articles

Constraining the number of positive responses in adaptive, non-adaptive, and two-stage group testing

Group testing is a well known search problem that consists in detecting the defective members of a set of objects O by performing tests on properly chosen subsets (pools) of the given set O. In classical group testing the goal is to find all defectives by using as few tests as possible. We consider a variant of classical group testing in which one is concerned not only with minimizing the total number of tests but aims also at reducing the number of tests involving defective elements. The rationale behind this search model is that in many practical applications the devices used for the tests are subject to deterioration due to exposure to or interaction with the defective elements. In this paper we consider adaptive, non-adaptive and two-stage group testing. For all three considered scenarios, we derive upper and lower bounds on the number of “yes” responses that must be admitted by any strategy performing at most a certain number t of tests. In particular, for the adaptive case we provide an algorithm that uses a number of “yes” responses that exceeds the given lower bound by a small constant. Interestingly, this bound can be asymptotically attained also by our two-stage algorithm, which is a phenomenon analogous to the one occurring in classical group testing. For the non-adaptive scenario we give almost matching upper and lower bounds on the number of “yes” responses. In particular, we give two constructions both achieving the same asymptotic bound. An interesting feature of one of these constructions is that it is an explicit construction. The bounds for the non-adaptive and the two-stage cases follow from the bounds on the optimal sizes of new variants of d-cover free families and (p, d)-cover free families introduced in this paper, which we believe may be of interest also in other contexts.

Sampling Plans Based on Truncated Life Test for a Generalized Inverted Exponential Distribution

In this paper, we propose a two-stage group acceptance sampling plan for generalized inverted exponential distribution under truncated life test. Median life is considered as a quality parameter. Design parameters are obtained to ensure that true median life is longer than a given specified life at certain level of consumer’s risk and producer’s risk. We also explore situations under which design parameters based on median lifetime can be used for other percentile points. Tables and specific examples are reported to explain the proposed plans. Finally a real data set is analyzed to implement the plans in practical situations and some suggestions are given.

Results of the modified bi-pectoral muscle flap procedure for post-sternotomy deep wound infection.

Post-sternotomy deep sternal wound infection (DSWI) is a severe complication of cardiac surgery. The introduction of omental and muscle flaps has resulted in a significant decrease in morbidity and mortality. In this article, we present the findings for a series of 55 consecutive patients with DSWI treated using an alternative bi-pectoral musculofascial flap technique. The patients were stratified into two groups (one-or two-stage intervention). Patients with septic wounds initially underwent debridement and wound treatment, while vacuum therapy was used in a subset of the subjects. All patients were treated with wound debridement and bi-pectoral advancement flap reconstruction. 30-day mortality was 5.4%. Most patients (72%) were treated in two stages, while vacuum therapy was used in 20% of the patients. The mean number of hospitalization days was 8 and 12 for the one- and the two-stage groups, respectively. Reconstruction was successful in all but three patients, each of whom developed recurrent infection. No major morbidity was reported at a mean follow-up of 82 months with excellent functional and aesthetic outcomes. Pectoralis-major muscle flaps remain relevant in the modern management of post-sternotomy mediastinitis. The addition of an omental flap should be considered in cases in which the lower sternum is involved. Prompt diagnosis and a meticulous surgical technique ensure favorable results for the majority of patients.

Bilateral anterior shoulder instability: epidemiology and results after bilateral open Latarjet procedure

There are no reports in the current literature involving a larger series of patients with bilateral shoulder instability. Descriptive analysis of a cohort of 75 patients (67M/8F) with surgically treated bilateral anterior shoulder instability. Clinical and radiological outcome was assessed in a subgroup of 16 patients at a minimum follow-up of 2 years following bilateral Latarjet procedures. The mean age at onset of instability was 20 years and 25 years at the time of surgery. Seventy-two patients played contact or over-head sports. In 67 patients, instability was traumatic in etiology. Hyperlaxity was present in 21 cases. Bankart lesions were identified in all shoulders, glenoid bone loss in 67 and humeral bone loss in 60. Surgery was performed in “one-stage” (5–21 days between procedures) in 27 patients and in “two-stages” in 48 (mean 36.7 months between procedures). At 1-year and at final follow-up (mean 153 months) postoperatively, the mean Walch–Duplay score in those who underwent one-stage treatment was 76 and 82, respectively, compared to 78 and 69 in those treated in two stages. The mean subjective shoulder value in the one-stage group was 87 % at one year and 93 % at final follow-up compared with 92 % and 93 % for the two-stage group. All but one patient in each group was either satisfied or very satisfied with the outcome following surgery. Return to sport at the preoperative level was possible in 56 % of patients. Recurrence of instability was observed in one patient following one-stage treatment compared to three cases in those treated in two-stages. In this cohort of patients, bilateral anterior shoulder instability was primarily traumatic in origin and was more frequently observed in young males involved in contact and overhead sporting activities. There was no clear advantage to adopting a one-stage strategy rather than performing surgical intervention in two separate stages.

Review of transposed basilic vein access for hemodialysis.

There is ongoing debate about the use of transposed basilic vein (TBV) fistula and the choice between it and prosthetic arteriovenous graft (AVG). This paper reviews the available literature relating to TBV fistula in terms of surgical technique, patency rates, complications, access survival and compares it with prosthetic AVG for hemodialysis (HD). Review of English language publications on TBV during the last two decades. The rate of fistula maturation was higher in the two-stage group, although the mean diameter of the basilic vein was smaller. Dialysis via central venous catheters at time of surgery was most prevalent in patients undergoing staged procedures—14% in one-stage TBV and 43% in two-stage TBV. Several authors report 1-year cumulative patency rate of 47% to 96% and 59% to 90% for TBV and AVG, respectively. TBV provides a more cost-effective option and should be considered the next choice when primary autogenous fistulae are not possible, whereas AVGs are easier to create, can be punctured earlier and have a greater reintervention rate if the access fails. This analysis shows that TBV has several advantages over AVG and provides a valuable access for HD but raises the need for a comparative trial between TBV and the newer generation AVGs. There is no clear superiority of the one-stage over the two-stage procedure.

Limited experience, high body mass index and previous urethral surgery are risk factors for failure in open urethroplasty due to penile strictures

Objective. The aim of this study was to evaluate outcomes and possible risk factors for failure of open urethroplasty due to penile urethral strictures. Materials and methods. A retrospective chart review was undertaken of 90 patients with penile stricture undergoing 109 open urethroplasties between 2000 and 2011. In 80 urethroplasties, a one-stage procedure was performed: 68 of these had a pediculated penile skin flap, nine had a free buccal mucosal graft and three had a free skin graft. A two-stage procedure using buccal mucosa was performed in 29 urethroplasties. Failure was defined as when further urethral instrumentation was needed. Results. The mean age in the one-stage and two-stage groups were 50 and 54 years, respectively. The success rates in the corresponding groups were 65% and 72%, with follow-up times of 63 and 40 months, respectively. Multivariable analyses disclosed body mass index (BMI) and previous urethral surgery to be significant risk factors for failure in the one-stage group. Failure over time significantly decreased during the study period. Conclusions. Both one- and two-stage penile urethroplasty demonstrated success rates in line with previous reports. Limited experience, high BMI and previous urethral surgery appear to be associated with less favourable outcome.

A Note on the Minimax Solution for the Two-Stage Group Testing Problem

Group testing is an active area of current research and has important applications in medicine, biotechnology, genetics, and product testing. There have been recent advances in design and estimation, but the simple Dorfman procedure introduced by R. Dorfman in 1943 is widely used in practice. In many practical situations, the exact value of the probability p of being affected is unknown. We present both minimax and Bayesian solutions for the group size problem when p is unknown. For unbounded p, we show that the minimax solution for group size is 8, while using a Bayesian strategy with Jeffreys’ prior results in a group size of 13. We also present solutions when p is bounded from above. For the practitioner, we propose strong justification for using a group size of between 8 and 13 when a constraint on p is not incorporated and provide useable code for computing the minimax group size under a constrained p.

Cost-effectiveness of one-stage versus two-stage breast reconstruction in the United Kingdom

Aim: Permanent expanders allow for breast reconstruction as a single stage. These prostheses are more expensive than conventional tissue expanders, but this excess cost is markedly offset as only one operation is required. However, if the revision rate is sufficiently high, then this effect is negated. We aim to compare costs of one-stage vs . two-stage reconstruction at a single center, taking into account explantation and unexpected admissions following complications. Methods: A retrospective review was carried out on all patients who underwent one-stage and two-stage reconstruction over a 5-year period by a single surgeon. A cost analysis was performed taking into account, explantation and additional admissions. Results: One hundred and forty-three one-stage and 45 two-stage procedures were included. The explantation rate for one-stage procedures is 36%, at a mean of 12.9 months postimplantation, the majority of which were exchanged for silicone implants to improve cosmesis. Four (9%) of the two-stage procedures were explanted a mean of 18 months postreconstruction. Overall, one-stage reconstructions were significantly more expensive than the two-stage group ( P = 0.016). Conclusion: There are many benefits of one-stage breast reconstruction. However, it does not appear to be cost-effective when additional admissions for explantation surgery are taken into account.

Long-term outcome of cochlear implant in patients with chronic otitis media: one-stage surgery is equivalent to two-stage surgery.

This study compared long-term speech performance after cochlear implantation (CI) between surgical strategies in patients with chronic otitis media (COM). Thirty patients with available open-set sentence scores measured more than 2 yr postoperatively were included: 17 who received one-stage surgeries (One-stage group), and the other 13 underwent two-stage surgeries (Two-stage group). Preoperative inflammatory status, intraoperative procedures, postoperative outcomes were compared. Among 17 patients in One-stage group, 12 underwent CI accompanied with the eradication of inflammation; CI without eradicating inflammation was performed on 3 patients; 2 underwent CIs via the transcanal approach. Thirteen patients in Two-stage group received the complete eradication of inflammation as first-stage surgery, and CI was performed as second-stage surgery after a mean interval of 8.2 months. Additional control of inflammation was performed in 2 patients at second-stage surgery for cavity problem and cholesteatoma, respectively. There were 2 cases of electrode exposure as postoperative complication in the two-stage group; new electrode arrays were inserted and covered by local flaps. The open-set sentence scores of Two-stage group were not significantly higher than those of One-stage group at 1, 2, 3, and 5 yr postoperatively. Postoperative long-term speech performance is equivalent when either of two surgical strategies is used to treat appropriately selected candidates.

Percutaneous transhepatic biliary metal stent for malignant hilar obstruction: results and predictive factors for efficacy in 159 patients from a single center.

To investigate and compare the efficacy and safety of percutaneous transhepatic biliary stenting (PTBS) using a one- or two-stage procedure and determine the predictive factors for the efficacious treatment of malignant hilar obstruction (MHO). 159 consecutive patients with MHO who underwent PTBS were enrolled between January 2010 and June 2013. Patients were classified into one- or two-stage groups. Independent predictors of therapeutic success were evaluated using a logistic regression model. 108 patients were treated with one-stage PTBS and 51 patients were treated with two-stage PTBS. The stents were technically successful in all patients. Successful drainage was achieved in 114 patients (71.4 %). A total of 42 early major complications were observed. Re-interventions were attempted in 23 patients during follow-up. The cumulative primary patency rates at 3, 6, and 12 months were 88, 71, and 48 %, respectively. Stent placement using a one- or two-stage procedure did not significantly affect therapeutic success, early major complications, median stent patency, or survival. A stent placed across the duodenal papilla was an independent predictor of therapeutic success (odds ratio = 0.262, 95 % confidence interval [0.107-0.642]). Patients with stents across papilla had a lower rate of cholangitis compared with patients who had a stent above papilla (7.1 vs. 20.3 %, respectively, p = 0.03). The majority of patients with MHO who underwent one-stage PTBS showed similar efficacy and safety outcomes compared with those who underwent two-stage PTBS. Stent placement across the duodenal papilla was associated with a higher therapeutic success rate.

A group decision-making approach to uncertain quality function deployment based on fuzzy preference relation and fuzzy majority

Quality function deployment (QFD) is one of the very effective customer-driven quality system tools typically applied to fulfill customer needs or requirements (CRs). It is a crucial step in QFD to derive the prioritization of design requirements (DRs) from CRs for a product. However, effective prioritization of DRs is seriously challenged due to two types of uncertainties: human subjective perception and customer heterogeneity. This paper tries to propose a novel two-stage group decision-making approach to simultaneously address the two types of uncertainties underlying QFD. The first stage is to determine the fuzzy preference relations of different DRs with respect to each customer based on the order-based semantics of linguistic information. The second stage is to determine the prioritization of DRs by synthesizing all customers’ fuzzy preference relations into an overall one by fuzzy majority. Two examples, a Chinese restaurant and a flexible manufacturing system, are used to illustrate the proposed approach. The restaurant example is also used to compare with three existing approaches. Implementation results show that the proposed approach can eliminate the burden of quantifying qualitative concepts and model customer heterogeneity and design team’s preference. Due to its easiness, our approach can reduce the cognitive burden of QFD planning team and give a practical convenience in QFD planning. Extensions to the proposed approach are also given to address application contexts involving a wider set of HOQ elements.

Stepwise two‐stage sample size adaptation

Several adaptive design methods have been proposed to reestimate sample size using the observed treatment effect after an initial stage of a clinical trial while preserving the overall type I error at the time of the final analysis. One unfortunate property of the algorithms used in some methods is that they can be inverted to reveal the exact treatment effect at the interim analysis. We propose using a step function with an inverted U-shape of observed treatment difference for sample size reestimation to lessen the information on treatment effect revealed. This will be referred to as stepwise two-stage sample size adaptation. This method applies calculation methods used for group sequential designs. We minimize expected sample size among a class of these designs and compare efficiency with the fully optimized two-stage design, optimal two-stage group sequential design, and designs based on promising conditional power. The trade-off between efficiency versus the improved blinding of the interim treatment effect will be discussed.

Two-stage urethroplasty is a better choice for proximal hypospadias with severe chordee after urethral plate transection: a single-center experience.

It is still debatable whether single- or two-stage urethroplasty is a more suitable technique for treating hypospadias with severe chordee after urethral plate transection. This retrospective study evaluated these two techniques. A total of 66 patients of proximal hypospadias with severe chordee were divided into two groups according to the techniques they underwent: 32 and 34 patients underwent single-stage (Duckett) or two-stage urethroplasty, respectively. Median ages at presentation were 7.5 years and 11.0 years in single-stage and two-stage repair groups, respectively. Median follow-ups were 28.5 months (20−60 months) and 35 months (18−60 months) in the single-stage and two-stage groups, respectively. The meatus of the neourethra was located at the top of the glans in all patients. No recurrence of chordee was found during follow-up, and all patients or parents were satisfied with the penile length and appearance. Complications were encountered in eight patients in both groups, with no statistically significant differences between the two techniques. The late complication rate of stricture was higher after the single-stage procedure (18.75% vs 0%). The complication rate after single-stage repairs was significantly lower in the prepubescent subgroup (10.52%) than in the postpubescent cohort (46.15%). These results indicate that the urethral plate transection effectively corrects severe chordee associated with proximal hypospadias during the intermediate follow-up period. Considering the higher rate of stricture after single-stage urethroplasty, two-stage urethroplasty is recommended for proximal hypospadias with severe chordee after urethral plate transection.

Effects of weaning beef cattle in two stages or by abrupt separation on nasal abrasions, behaviour, and weight gain

The effects of traditional (n = 103) and two-stage weaning (n = 89) on nasal abrasions, behaviour, and weight gain were evaluated in a total of 192 cow-calf pairs. Two-stage calves were prevented from suckling by fitting nose flaps for 7 days before separation from their mothers. Nasal abrasions caused by the devices were assessed by scoring the irritations of the nasal septum at removal and 1 week later. The behaviour of 20 calves was observed for 3 days before and 4 days after weaning and vocalisations of the cows after separation were recorded. Nasal abrasions were found in more than 95% of the animals at removal, whereas 30% of the animals showed heavy bleeding and 10% suffered from even worse injuries. One week later, 45% of the calves still showed irritations. Cows of the traditional group vocalised 19.2 and those of the two-stage group 3.7 times per hour (P < 0.001). Compared with the pre-weaning period, calves spent more time walking on Days 1 and 2 after weaning (P < 0.01). However, the duration was significantly lower in two-stage than in traditionally weaned animals (P < 0.01). After removal of the devices, the time spent for walking increased again for 2 days. An effect on the weight gain of the calves was not noted. In conclusion, two-stage weaning positively influenced the post-weaning behaviour, but the nose flaps caused heavy nasal abrasions in the calves. Therefore, the design of the devices and the period they are fitted should be modified to minimise nasal abrasions.

Single-Stage vs. Two-Stage Management for Concomitant Gallstones and Common Bile Duct stones: A Prospective Randomized Trial with Long-Term Follow-up

AimThe preferred approach to the management of common bile duct (CBD) stones is uncertain, with single-stage laparoscopic cholecystectomy and CBD exploration vs. two-stage preoperative endoscopic CBD clearance followed by laparoscopic cholecystectomy being debated. To address this, a prospective randomized study which compared these two management strategies was undertaken. MethodsBetween Jan 2002 and Dec 2005, patients with gallstones and common bile duct stones diagnosed by preoperative ultrasonography and magnetic resonance cholangiopancreatography were randomized to single-stage vs. two-stage treatment. In a single-stage group, laparoscopic cholecystectomy and CBD exploration were undertaken at the same operation, whereas in a two-stage group, endoscopic stone clearance was followed by laparoscopic cholecystectomy 2–5 days later. Early treatment success and complications and longer-term follow-up for the two groups were compared. ResultsTwo hundred twenty-one patients were enrolled in the trial, 110 in the single-stage group and 111 in the two-stage group. There was no significant difference in the success rate of CBD clearance (93.6 vs. 94.6 %, p = 0.76) or the complication rates (3.6 vs. 5.1 %, p = 0.527) between the groups. However, at longer-term follow-up, recurrent CBD stones were seen more often in the two-stage group (9.5 vs. 2.1 %, p = 0.037). ConclusionThe single-stage and two-stage approaches were equally effective in achieving initial clearance of CBD stones. However, recurrent CBD stones occurred more commonly in patients who had undergone two-stage treatment with initial endoscopic stone clearance, followed by laparoscopic cholecystectomy.

Risk of developing metachronous colon neoplasm after polypectomy: comparison of one-stage versus two-stage polypectomy

The impact of one-stage polypectomy (removal of all neoplasms during diagnostic colonoscopy) versus two-stage polypectomy (removal of all neoplasms during therapeutic colonoscopy following the initial diagnostic colonoscopy) on the development of metachronous neoplasms is poorly understood. Our aim was to compare the effects of one- versus two-stage polypectomy on the development of metachronous neoplasms We retrospectively reviewed the medical records of 249 patients in a tertiary center who underwent one-stage polypectomy, which was followed by one or more surveillance colonoscopy. The development of metachronous neoplasm in this group was compared with that of an age- and sex-matched two-stage polypectomy group consisting of 498 patients In total, 346 (46.3 %) patients developed any metachronous neoplasm and 29 (3.9 %) patients developed advanced metachronous neoplasm. The 5 years cumulative incidences of any and advanced metachronous neoplasm were 46.2 and 5.0 %, respectively, in the one-stage group, which are not significantly different from the rates of 50.7 and 3.3 % in the two-stage group (p = 0.94 and 0.30, respectively). The only significant risk factor for developing any metachronous neoplasm was ≥ 3 neoplasms at the baseline polypectomy [hazard ratio (HR) 1.75; 95 % confidence interval (CI) 1.41-2.17; p < 0.001]. The only significant risk factor for developing advanced metachronous neoplasm was advanced neoplasm at the baseline polypectomy (HR 2.37; 95 % CI 1.16-4.84; p = 0.01). One- and two-stage polypectomy did not affect the development rates of metachronous neoplasm The risks of developing metachronous neoplasm may be similar following one- and two-stage polypectomy.

Screening Strategies in the Presence of Interactions

Product and process improvement can involve a large number of factors that must be varied simultaneously. Understanding how factors interact is a key step in identifying those factors that have a substantial impact on the response. This article gives the first comprehensive assessment and comparison of screening strategies for interactions using two-level supersaturated designs, group screening, and a variety of data analysis methods including shrinkage regression and Bayesian methods. We develop novel methodology to allow application of Bayesian methods in two-stage group screening. Insights on using the strategies are provided through a variety of simulation scenarios and open issues are discussed. Supplementary materials are available online.

Surgical therapy of extensive knee joint empyema: mid-term results after two-stage versus one-stage procedures

Untreated knee joint empyema leads to rapid destruction of the joint and, thus far, has proven challenging to treat. This study presents data obtained after one- versus two-stage surgical approaches. Specifically, clinical outcome, complication rate, re-infection rate, duration of operation, and hospital stay are reported. Between 2006 and 2010, 67 patients with extensive knee joint empyema underwent surgical therapy. Patients underwent either a two-stage surgical approach with open joint treatment for 7-10 days or a one-stage procedure with primary closure of the knee joint after radical debridement. The two-stage procedure was performed on 36 patients, whereas the one-stage procedure was performed on 31 patients. Infection duration prior to the index procedure ranged from 3 days to 55 months (two-stage: ~5 months, one-stage: ~2.4 months). The groups did not differ significantly in demographic group characteristics. Hospital stay and duration of operation were significantly (p < 0.01) reduced in the one-stage group compared to the two-stage group (31.1 ± 10.6 vs. 23.4 ± 14.4 days and 105 ± 32 vs. 68 ± 18 min, respectively). Functional outcome improved in both groups from the pre- to post-operative period, but did not differ significantly between groups. The one-stage open surgical approach produced similar results to the two-stage approach in the treatment of extensive knee joint empyemas. However, by waiving the open joint treatment concept, duration of hospital stay and operation time could be significantly reduced. III.

Skip-Lot Sampling Plan of Type SkSP-2 with Two-Stage Group Acceptance Sampling Plan as Reference Plan

This article deals with the optimal designing of skip-lot sampling plan of type SkSP-2 based on time-truncated life tests by considering two-stage group sampling plan as the reference plan under Burr type X and XII distributions. The optimal plan parameters are determined such that the specified producer's risk and consumer's risk are satisfied for given values of experiment time, percentile ratios, and percentile values. Extensive tables are also provided for various values of shape parameters. Examples reveal the use of the plan in laboratory experiments.

Extraoral implants for orbit rehabilitation: a comparison between one-stage and two-stage surgeries

The aim of the study was to compare the osseointegration success rate and time for delivery of the prosthesis among cases treated by two-stage or one-stage surgery for orbit rehabilitation between 2003 and 2011. Forty-five patients were included, 31 males and 14 females; 22 patients had two-stage surgery and 23 patients had one-stage surgery. A total 138 implants were installed, 42 (30.4%) on previously irradiated bone. The implant survival rate was 96.4%, with a success rate of 99.0% among non-irradiated patients and 90.5% among irradiated patients. Two-stage patients received 74 implants with a survival rate of 94.6% (four implants lost); one-stage surgery patients received 64 implants with a survival rate of 98.4% (one implant lost). The median time interval between implant fixation and delivery of the prosthesis for the two-stage group was 9.6 months and for the one-stage group was 4.0 months (P<0.001). The one-stage technique proved to be reliable and was associated with few risks and complications; the rate of successful osseointegration was similar to those reported in the literature. The one-stage technique should be considered a viable procedure that shortens the time to final rehabilitation and facilitates appropriate patient follow-up treatment.