3,624 research outputs found
Consistent Nonparametric Tests for Lorenz Dominance
This paper proposes a test for Lorenz dominance. Given independent samples of income or other welfare related variable, we propose a test of the null hypothesis that the Lorenz curve for one population is dominated by the Lorenz curve for a second population. The test statistic is based on the standardized largest difference between the empirical Lorenz curves for the two samples. The test is nonparametric in the sense that no distributional assumptions are made and the test is consistent because it compares the Lorenz curves at all quantiles. We derive the asymptotic distribution of the test statistic under the null hypothesis. Since the limiting distribution of the test statistic is nonstandard, being dependent on the underlying Lorenz curves, we propose the use of two computer based procedures for conducting inference. The first is a simulation method that simulates p-values from an approximation to the underlying limiting distribution of the statistic while the second is based on the nonparametric bootstrap. We examine the performance of the methods in a Monte Carlo study and with a comparison of the income based Lorenz curves for the US and Canada.Lorenz dominance, test consistency, simulation.
The Effect of College Curriculum on Earnings: Accounting for Non-Ignorable Non-Response Bias
We link information on the current earnings of college graduates from many cohorts to their high-school records, their detailed college records and their demographics to infer the impact of college major on earnings. We develop an estimator to handle the potential for non-response bias and identify non-response using an affinity measure -- the potential respondent's link to the organization conducting the survey. This technique is generally applicable for adjusting for unit non-response. In the model describing earnings, estimated using the identified (for non-response bias) selectivity adjustments, adjusted earnings differentials across college majors are less than half as large as unadjusted differentials and ten percent smaller than those that do not account for selective non-response.
On rank estimation in semidefinite matrices
This work concerns the problem of rank estimation in semidefinite matrices, having either indefinite or semidefinite matrix estimator satisfying a typical asymptotic normality condition. Several rank tests are examined, based on either available rank tests or basic new results. A number of related issues are discussed such as the choice of matrix estimators and rank tests based on finer assumptions than those of asymptotic normality of matrix estimators. Several examples where rank estimation in semidefinite matrices is of interest are studied and serve as guide throughout the work.rank, symmetric matrix, indefinite and semidefinite estimators, eigenvalues, matrix decompositions, estimation, asymptotic normality.
Local and global rank tests for multivariate varying-coefficient models
In a multivariate varying-coefficient model, the response vectors Y are regressed on known functions u(X) of some explanatory variables X and the coefficients in an unknown regression matrix q(Z) depend on another set of explanatory variables Z. We provide statistical tests, called local and global rank tests, which allow to estimate the rank of an unknown regression coefficient matrix q(Z) locally at a fixed level of the variable Z or globally as the maximum rank over all levels of Z, respectively. In the case of local rank tests, we do so by applying already available rank tests to a kernel-based estimator of the coefficient matrix q(z). Global rank tests are obtained by integrating test statistics used in estimation of local rank tests. We present a simulation study where, focusing on global ranks, we examine small sample properties of the considered statistical tests. We also apply our results to estimate the so-called local and global ranks in a demand system where budget shares are regressed on known functions of total expenditures and the coefficients in a regression matrix depend on prices faced by a consumer.varying-coefficient model, kernel smoothing, matrix rank estimation, demand systems, local and global ranks
Enhanced recovery after surgery
Enhanced Recovery or Fast Track Recovery after Surgery protocols (ERAS) have significantly changed perioperative care following colorectal surgery and are promoted as reducing the stress response to surgery.
The present systematic review aimed to examine the impact on the magnitude of the systemic inflammatory response (SIR) for each ERAS component following colorectal surgery using objective markers such as C-reactive protein (CRP) and interleukin-6 (IL-6).
A literature search was performed of the US National Library of Medicine (MEDLINE), EMBASE, PubMed, and the Cochrane Database of Systematic Reviews using appropriate keywords and subject headings to February 2015.
Included studies had to assess the impact of the selected ERAS component on the SIR using either CRP or IL-6.
Nineteen studies, including 1898 patients, were included. Fourteen studies (1246 patients) examined the impact of laparoscopic surgery on the postoperative markers of SIR. Ten of these studies (1040 patients) reported that laparoscopic surgery reduced postoperative CRP. One study (53 patients) reported reduced postoperative CRP using opioid-minimising analgesia. One study (142 patients) reported no change in postoperative CRP following preoperative carbohydrate loading. Two studies (108 patients) reported conflicting results with respect to the impact of goal-directed fluid therapy on postoperative IL-6. No studies examined the effect of other ERAS components, including mechanical bowel preparation, antibiotic prophylaxis, thromboprophylaxis, and avoidance of nasogastric tubes and peritoneal drains on markers of the postoperative SIR following colorectal surgery.
The present systematic review shows that, with the exception of laparoscopic surgery, objective evidence of the effect of individual components of ERAS protocols in reducing the stress response following colorectal surgery is limited
The impact of preoperative dexamethasone on the magnitude of the postoperative systemic inflammatory response and complications following surgery for colorectal cancer
Background:
The magnitude of the postoperative systemic inflammatory response (SIR), as evidenced by C-reactive protein (CRP), is associated with both short- and long-term outcomes following surgery for colorectal cancer. The present study examined the impact of preoperative dexamethasone on the postoperative SIR and complications following elective surgery for colorectal cancer.
Methods:
Patients who underwent elective surgery, with curative intent, for colorectal cancer at a single center between 2008 and 2016 were included (n = 556) in this study. Data on the use of preoperative dexamethasone were obtained from anesthetic records, and its impact on CRP on postoperative days (PODs) 3 and 4, as well as postoperative complications, was assessed using propensity score matching (n = 276).
Results:
In the propensity score-matched cohort, preoperative dexamethasone was associated with fewer patients exceeding the established CRP threshold of 150 mg/L on POD 3 (odds ratio [OR] 0.42, 95% confidence interval [CI] 0.26ā0.70, p < 0.001) and fewer postoperative complications (OR 0.53, 95% CI 0.33ā0.86, p = 0.009). Similar results for both POD 3 CRP and complications were observed when using propensity score-adjusted regression (OR 0.40, 95% CI 0.28ā0.57 and OR 0.57, 95% CI 0.41ā0.80, respectively) and propensity score stratification (OR 0.41, 95% CI 0.25ā0.57 and OR 0.53, 95% CI 0.33ā0.86, respectively).
Conclusions:
Preoperative dexamethasone was associated with a lower postoperative SIR and fewer complications following elective surgery for colorectal cancer
The relationship between cardiopulmonary exercise test variables, the systemic inflammatory response, and complications following surgery for colorectal cancer
Background:
Both preoperative cardiopulmonary exercise test (CPET)-derived measures of fitness and postoperative C-reactive protein (CRP) concentrations are associated with complications following surgery for colorectal cancer. The aim of the present pilot study was to examine the relationship between CPET and postoperative CRP concentrations in this patient group.
Methods:
Patients who had undergone CPET prior to elective surgery for histologically confirmed colorectal cancer in a single centre between September 2008 and April 2017 were included. Preoperative VO2 at the anaerobic threshold (AT) and peak exercise were recorded, along with preoperative modified Glasgow Prognostic Score (mGPS) and CRP on each postoperative day.
Results:
Thirty-eight patients were included. The majority were male (30, 79%), over 65 years old (30, 79%), with colonic cancer (23, 61%) and node-negative disease (24, 63%). Fourteen patients (37%) had open surgery and 24 (63%) had a laparoscopic resection. A progressive reduction in VO2 at peak exercise was significantly associated with both increasing American Society of Anesthesiology (ASA) grade (median, ml/kg/min: ASA 1ā=ā22, ASA 2ā=ā19, ASA 3ā=ā15, ASA 4ā=ā12, pā=ā0.014) and increasing mGPS (median, ml/kg/min: mGPS 0ā=ā18, mGPS 1ā=ā16, mGPSā2 = 14, pā=ā0.039) There was no significant association between either VO2 at the AT or peak exercise and postoperative CRP.
Conclusions:
The present pilot study reports a possible association between preoperative CPET-derived measures of exercise tolerance, and the preoperative systemic inflammatory response, but not postoperative CRP in patients undergoing surgery for colorectal cancer
The relationship between systemic inflammation and stoma formation following anterior resection for rectal cancer: a cross-sectional study
Introduction:
There is evidence that temporary defunctioning stoma formation in patients undergoing anterior resection reduces the risk of anastomotic leakage. The aim of the present study was to investigate the relationship between stoma formation, the postoperative systemic inflammatory response and complications following anterior resection for rectal cancer.
Methods:
Data was recorded prospectively for patients who underwent anterior resection for histologically proven rectal cancer, from 2008 to 2015Ā at a single centre, nĀ =Ā 167. Patients had routine preoperative and postoperative blood sampling including serum C-reactive protein (CRP). Postoperative complications including anastomotic leakage were recorded.
Results:
Of the 167 patients, the majority were male (61%) and over 65 years old (56%) with node negative disease (60%). 36 patients (22%) underwent preoperative neoadjuvant treatment. 100 patients (60%) had a stoma formed at the time of surgery. Stoma formation was significantly associated with male sex (69% vs. 50%, pĀ =Ā 0.017), neoadjuvant chemoradiotherapy (30% vs 9%, pĀ =Ā 0.001) and open surgery (71% vs. 55%, pĀ =Ā 0.040). Of those 100 patients who had a stoma formed, 80 had it reversed. Permanent stoma was significantly associated with increasing age (pĀ =Ā 0.011), exceeding the established CRP threshold of 150Ā mg/L on postoperative day 4 (67% vs 37%, pĀ =Ā 0.039), higher incidence of postoperative complications (76% vs 47%, pĀ =Ā 0.035), anastomotic leakage (24% vs 2%, pĀ =Ā 0.003) and higher Clavien Dindo score (pĀ =Ā 0.036).
Conclusions:
There was no significant association between stoma formation during anterior resection and the postoperative systemic inflammatory response. However, in these patients both the postoperative systemic inflammatory response and complications were associated with permanent stoma
Attitudes of surgeons to the use of postoperative markers of the systemic inflammatory response following elective surgery
Background:
Cancer is responsible for 7.6 million deaths worldwide and surgery is the primary modality of a curative outcome. Postoperative care is of considerable importance and it is against this backdrop that a questionnaire based study assessing the attitudes of surgeons to monitoring postoperative systemic inflammation was carried out.
Method:
A Web based survey including 10 questions on the āattitudes of surgeons to the use of postoperative markers of the systemic inflammatory response following elective surgeryā was distributed via email. Two cohorts were approached to participate in the survey. Cohort 1 consisted of 1092 surgeons on the āAssociation of Coloproctology of Great Britain and Ireland (ACPGBI)ā membership list. Cohort 2 consisted of 270 surgeons who had published in this field in the past as identified by two recent reviews. A reminder email was sent out 21 days after the initial email in both cases and the survey was closed after 42 days in both cases.
Result:
In total 29 surgeons (2.7%) from cohort 1 and 40 surgeons (14.8%) from cohort 2 responded to the survey. The majority of responders were from Europe (77%), were colorectal specialists (64%) and were consultants (84%) and worked in teaching hospitals (54%) and used minimally invasive techniques (87%). The majority of responders measured CRP routinely in the post-operative period (85%) and used CRP to guide their decision making (91%) and believed that CRP monitoring should be incorporated into postoperative guidelines (81%).
Conclusion:
Although there was a limited response the majority of surgeons surveyed measure the systemic inflammatory response following elective surgery and use CRP measurements together with clinical findings to guide postoperative care. The present results provide a baseline against which future surveys can be compared
Identification, Estimation, and Testing in Empirical Models of Auctions Within the Independent Private Values Paradigm
- ā¦