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Concept: Statistical tests


Obesity has been associated with respiratory complications, and the majority of these complications occur in the Post-Anesthesia Care Unit (PACU). The aim of this study was to evaluate the outcome and incidence of adverse respiratory events (AREs) in obese patients during their stay in the PACU METHODS: We conducted a prospective control study that included 27 obese patients matched with an equal number of patients with body mass index (BMI)<30 (non-obese control group); the 2 groups of patients were similar in respect to gender distribution, age, and type of surgery and had been admitted into the PACU after elective surgery (May 2011). The AREs were identified during PACU stay. Descriptive analysis of variables was performed, and the Mann-Whitney U test, Chi-square test, or Fisher's exact test were used for comparisons. Associations with AREs were studied using univariate and multivariate logistic regression models.

Concepts: Categorical data, Mann–Whitney U, Chi-square test, Body mass index, Statistics, Fisher's exact test, Statistical tests, Non-parametric statistics


The primary objective of this study was to investigate if differences in dog bite characteristics exist amongst legislated and non-legislated dog breeds listed under breed-specific legislation in Ireland (age when bitten, anatomical bite locations, triggers for biting, victim’s relationship with the dog, geographical location and owner presence, history of aggression, reporting bite incident to authorities, medical treatment required following the bite, and type of bite inflicted). A second objective of the current study was to investigate dog control officer’s enforcement and perceptions of current legislation. Data for statistical analyses were collated through a nationally advertised survey, with Pearson Chi-square and Fisher’s Exact Test statistical methods employed for analyses. A total of 140 incident surveys were assessed comprising of non-legislated (n = 100) and legislated (n = 40) dog bite incidents.

Concepts: Injuries, Exact test, Statistics, Chi-square test, Ronald Fisher, Statistical tests, Bite, Fisher's exact test


BACKGROUND:Between 1992 and 2011, 373 Canadian individuals with adverse anesthetic reaction were referred to the Malignant Hyperthermia Unit in Toronto, Ontario, Canada for malignant hyperthermia (MH) diagnostic testing. We analyzed the epidemiologic characteristics of the index adverse anesthetics for those probands who were confirmed to be MH susceptible.METHODS:One hundred twenty-nine proband survivors of adverse anesthetic reactions, whose MH susceptible status was confirmed by caffeine-halothane contracture testing were selected. Individuals were excluded if the index anesthetic record was not available for review. Data regarding demographics, clinical signs, laboratory findings, treatment, and complications were retrospectively compiled and analyzed. A Fisher exact test and χ(2) test were applied to compare categorical variables. The Wilcoxon rank-sum test was applied with continuous variables.RESULTS:Young males (61.2%) dominated among selected patients. Seventeen of 129 (13.2%) patients had prior unremarkable anesthesia. Anesthetic triggers were volatile-only (n = 58), succinylcholine-only (n = 20), or both volatile and succinylcholine (n = 51). Eight (6.2%) cases occurred in the postanesthetic care unit. There were no reactions after discharge from the postanesthetic care unit. The most frequent clinical signs were hyperthermia (66.7%), sinus tachycardia (62.0%), and hypercarbia (51.9%). Complications occurred in 20.1% of patients, the most common complication being renal dysfunction. When 20 or more minutes between the first adverse sign and dantrolene treatment elapsed, complication rates increased to ≥30%.CONCLUSIONS:This is the first Canadian study in 3 decades to report nationwide data on MH epidemiology. Features that differ from earlier reports include a 15.5% incidence of reactions triggered by succinylcholine alone and lower complication rates. In agreement with previously published studies, we confirmed in this independent dataset that increased complication rates were associated with an increased time interval between the first adverse clinical sign and dantrolene treatment. This underscores the need for early diagnosis and rapid dantrolene access and administration in anesthetizing locations using either succinylcholine or volatile anesthetic drugs.

Concepts: Ketamine, Statistical tests, Fever, Local anesthetic, Anesthesia, Anesthetics, Anesthetic, Malignant hyperthermia


Background: Suicide clusters at Cornell University and the Massachusetts Institute of Technology (MIT) prompted popular and expert speculation of suicide contagion. However, some clustering is to be expected in any random process. Aim: This work tested whether suicide clusters at these two universities differed significantly from those expected under a homogeneous Poisson process, in which suicides occur randomly and independently of one another. Method: Suicide dates were collected for MIT and Cornell for 1990-2012. The Anderson-Darling statistic was used to test the goodness-of-fit of the intervals between suicides to distribution expected under the Poisson process. Results: Suicides at MIT were consistent with the homogeneous Poisson process, while those at Cornell showed clustering inconsistent with such a process (p = .05). Conclusions: The Anderson-Darling test provides a statistically powerful means to identify suicide clustering in small samples. Practitioners can use this method to test for clustering in relevant communities. The difference in clustering behavior between the two institutions suggests that more institutions should be studied to determine the prevalence of suicide clustering in universities and its causes.

Concepts: Arithmetic mean, Random variable, Statistical tests, Cornell University, Anderson–Darling test, Probability theory, Kolmogorov–Smirnov test, Normal distribution


Aseptic techniques are required to manipulate central venous lines and prepare intravenous doses. This study aimed to examine whether different aseptic techniques affect the contamination rates of intravenous doses prepared on hospital wards. Syringes of tryptic soy broth test media prepared by one pharmacy operator and five nurses were assessed for contamination. The pharmacy operator achieved lower contamination than the nurses (0.0% vs 6.9%; Fisher’s exact test, P < 0.001). Contamination differed significantly between nurses (∼2-17% of syringes; binary logistic regression, P = 0.018). In conclusion, appropriate training and experience in aseptic techniques should be embedded into routine clinical practice to reduce contamination rates.

Concepts: Categorical data, Ronald Fisher, Regression analysis, Aseptic technique, Statistical tests, Logistic regression, Exact test, Fisher's exact test


Abstract Background: Recurrent herniation is a well-known complication following the initial repair of congenital diaphragmatic hernias (CDHs). The role of minimally invasive surgical techniques in recurrent CDH remains undefined. The purpose of this study was to evaluate our early experience with thoracoscopic repair compared with traditional open repair in children with recurrent CDH. Subjects and Methods: We retrospectively reviewed all recurrent Bochdalek CDH cases (n=24) managed at a single tertiary-care referral center between January 1990 and March 2011. Children who underwent thoracoscopic repair for recurrent CDH were identified, and their data were compared by the unpaired t test and the two-sided Fisher’s exact test, as appropriate, with those of children who underwent open repair. Significance was defined as P<.05. Results: Thoracoscopic repair was attempted in 6 (25%) children with recurrent CDH. Four (67%) repairs were successfully completed without conversion to an open procedure. The mean age at thoracoscopic repair was 11.5 months (range, 8.1-16.1 months). The mean operative time was 191 minutes (range, 94-296 minutes), and all children were extubated within 24 hours. The mean hospital length of stay was 3.75 days (range, 1-6 days). There were no deaths or subsequent recurrences after a mean follow-up of 26.5 months (range, 14.3-41.3 months). There were no statistical differences in any of the measured outcome variables when compared with the open repair group. Conclusions: Our initial experience suggests that thoracoscopic repair is a feasible alternative to open repair in selected children with recurrent Bochdalek diaphragmatic hernias.

Concepts: Statistical significance, Statistics, Ronald Fisher, Statistical tests, Exact test, Surgery, Congenital diaphragmatic hernia, Fisher's exact test


Abstract A microanastomosis might tolerate a torsion up to 360°, but the effects of arterial microanastomosis torsion on the survival of the flap it supplies are unclear. The aim of this study was to investigate the consequences of microarterial anastomosis torsion on the groin flap in rats. Forty Sprague-Dawley rats were divided into five groups. An oblique groin flap was harvested as an island flap and a patch-to-side arterial anastomosis was performed with torsion angles of 0°, 90°, 180°, 270°, and 360°. Six of eight flaps in Group I (0° torsion), six of eight flaps in Group II (90°), three of eight flaps in Group III (180°), and none of the flaps in Groups IV and V (270° and 360°) were found to be viable after 1 week. The patency and flap survival rates observed in Groups II, III, IV, and V were compared with those in Group I using Fisher’s exact test. The patency rates and flap survival rates in Groups IV and V were significantly lower compared with those in Group I. Our data show that skin flaps can survive even if their arterial pedicle is anastomosed with a torsion of up to 180°.

Concepts: Ronald Fisher, Group, Statistical tests, Anastomosis, Exact test, Fisher's exact test


This study aimed at examining three tilt angle-based positive responses and the time to positive response in a head-up tilt test for children with orthostatic intolerance, and the psychological fear experienced at the three angles during head-up tilt test. A total of 174 children, including 76 boys and 98 girls, aged from 4 to 18 years old (mean 11.3±2.8 years old), with unexplained syncope, were randomly divided into three groups, to undergo head-up tilt test at the angles of 60°, 70° and 80°, respectively. The diagnostic rates and times were analysed, and Wong-Baker face pain rating scale was used to access the children’s psychological fear. There were no significant differences in diagnostic rates of postural orthostatic tachycardia syndrome and vasovagal syncope at different tilt angles during the head-up tilt test (p>0.05). There was a significant difference, however, in the psychological fear at different tilt angles utilising the Kruskal-Wallis test (χ2=36.398, p<0.01). It was mildest at tilt angle 60° utilising the Kolmogorov-Smirnov test (p<0.01). A positive rank correlation was found between the psychological fear and the degree of tilt angle (rs=0.445, p<0.01). Positive response appearance time was 15.1±14.0 minutes at 60° for vasovagal syncope children. There was no significant difference in the time to positive response, at different tilt angles during the head-up tilt test for vasovagal syncope or for postural orthostatic tachycardia syndrome. Hence, it is suggested that a tilt angle of 60° and head-up tilt test time of 45 minutes should be suitable for children with vasovagal syncope.

Concepts: Difference, Orthostatic intolerance, Statistical tests, Cardiology, Statistical significance, Orthostatic hypotension, Non-parametric statistics, Postural orthostatic tachycardia syndrome


ObjectivesLoosening and loss rates of monocortical mini-implants are relatively high, therefore the following null hypothesis was tested: ‘The local bone stress in mono and bicortically-anchored mini-implants is identical’.Material and MethodsAnisotropic Finite Element Method (FEM) models of the mandibular bone, including teeth, periodontal ligaments, orthodontic braces, and mini-implants of varying length, were created. The morphology was based on the Computed Tomography data of an anatomical preparation. All mini-implants with varying insertion depths (monocortical short, monocortical long, bicortical) were typically loaded, and the induced effective stress was calculated in the cervical area of the cortical bone. The obtained values were subsequently analysed descriptively and exploratively using the SPSS 19.0 software.ResultsThe null hypothesis was rejected, since the stress values of each anchorage type differed significantly (Kruskal-Wallis Test, P < 0.001). Therefore, the lowest effective stress values were induced in bicortical anchorage (mean = 0.65MPa, SD = 0.06MPa) and the highest were induced in monocortical (short) anchorage of the mini-implants (mean = 1.79MPa, SD = 0.29MPa). The Spearman rank correlation was 0.821 (P < 0.001).ConclusionsThe deeper the mini-implant was anchored, the lower were the effective stress values in the cervical region of the cortical bone. Bicortical implant anchorage is biomechanically more favourable than monocortical anchorage; therefore, bicortical anchorage should be especially considered in challenging clinical situations requiring heavy anchorage.

Concepts: Finite element method in structural mechanics, Orthodontics, Statistical tests, Null hypothesis, Spearman's rank correlation coefficient, Non-parametric statistics, Finite element method


In a retrospective multicentre study, the success rate and efficiency of activator treatment were analysed. All patients from two University clinics (Giessen, Germany and Berne, Switzerland) that fulfilled the selection criteria (Class II division 1 malocclusion, activator treatment, no aplasia, no extraction of permanent teeth, no syndromes, no previous orthodontic treatment except transverse maxillary expansion, full available records) were included in the study. The subject material amounted to 222 patients with a mean age of 10.6 years. Patient records, lateral head films, and dental casts were evaluated. Treatment was classified as successful if the molar relationship improved by at least half to three-fourths cusp width depending on whether or not the leeway space was used during treatment. Group comparisons were carried out using Wilcoxon two-sample and Kruskal-Wallis tests. For discrete data, chi-square analysis was used and Fisher’s exact test when the sample size was small. Stepwise logistic regression was also employed. The success rate was 64 per cent in Giessen and 66 per cent in Berne. The only factor that significantly (P¡0:001) influenced treatment success was the level of co-operation. In approximately 27 per cent of the patients at both centres, the post-treatment occlusion was an ideal Class I. In an additional 38 per cent of the patients, marked improvements in occlusal relationships were found. In subjects with Class II division 1 malocclusions, in which orthodontic treatment is performed by means of activators, a marked improvement of the Class II dental arch relationships can be expected in approximately 65% of subjects. Activator treatment is more efficient in the late than in the early mixed dentition.

Concepts: Class II railroad, Non-parametric statistics, Statistical tests, Teeth, Orthodontics, Chi-square test, Fisher's exact test, Malocclusion