The likelihood that a study will yield statistically significant results depends on the chosen sample size. Surveillance and diagnostic situations that require sample size calculations include certification of disease freedom, estimation of diagnostic accuracy, comparison of diagnostic accuracy, and determining equivalency of test accuracy. Reasons for inadequately sized studies that do not achieve statistical significance include failure to perform sample size calculations, selecting sample size based on convenience, insufficient funding for the study, and inefficient utilization of available funding. Sample sizes are directly dependent on the assumptions used for their calculation. Investigators must first specify the likely values of the parameters that they wish to estimate as their best guess prior to study initiation. They further need to define the desired precision of the estimate and allowable error levels. Type I (alpha) and type II (beta) errors are the errors associated with rejection of the null hypothesis when it is true and the nonrejection of the null hypothesis when it is false (a specific alternative hypothesis is true), respectively. Calculated sample sizes should be increased by the number of animals that are expected to be lost over the course of the study. Free software routines are available to calculate the necessary sample sizes for many surveillance and diagnostic situations. The objectives of the present article are to briefly discuss the statistical theory behind sample size calculations and provide practical tools and instruction for their calculation.

Chronic diarrhea (CD) is common in dogs, and information on frequency and distribution of primary and secondary causes is lacking. To evaluate underlying causes and predictors of outcome in dogs with CD. One hundred and thirty-six client-owned dogs with CD (≥3 weeks duration). Retrospective review of medical records (Small Animal Clinic, Freie Universität Berlin, Germany, 09/2009-07/2011). Quantification of final diagnoses and comparison of clinical aspects including disease severity and clinicopathological abnormalities among dogs with clinical remission (either complete [gastrointestinal signs absent] or partial [clinical improvement of gastrointestinal signs and reduced episodes with shortened duration]), and those without recovery. Ninety percent of dogs were diagnosed with a primary enteropathy: inflammatory (71%; of those 66% dietary responsive, 23% idiopathic, 11% antibiotic responsive), infectious (13%), neoplastic (4%), and in one dog each mechanical disease or systemic vasculitis. Secondary causes were diagnosed in 10% of dogs: exocrine pancreatic (6%), endocrine (2%), and in one dog each hepatic, renal, and cardiac disease. In total, 87% of dogs had clinical remission, whereas 13% died or did not respond to treatment: Lack of recovery was frequently recorded for dogs with primary inflammatory (idiopathic) or neoplastic disease and was significantly associated with increased disease severity scores (P = .005), anemia (hematocrit < 40%, P < .001), severe hypoalbuminemia (serum albumin <2.0 g/dL, P = .008), and severe hypocobalaminemia (serum cobalamin concentration <200 pg/mL, P = .006). Inflammatory enteropathies and particularly those of dietary origin were the most common causes of CD in dogs. Findings support the usefulness of hematocrit, and serum albumin and cobalamin concentration as prognostic markers in dogs with CD.

Objective: To estimate the relative accuracy of a thoracic focused assessment with sonography for trauma (TFAST) protocol for rapid diagnosis of pneumothorax (PTX) and other thoracic injury in traumatized dogs.Design: Prospective case series.Setting: Private veterinary emergency center.Animals: One hundred and forty‐five client‐owned dogs evaluated within 24‐hours of injury.Interventions: Thoracic focused assessment with sonography for trauma protocol.Measurements and Main Results: Traumatized dogs were evaluated with a conventional ultrasound (US) machine using a standardized 4‐point thoracic FAST protocol before thoracic radiography (CXR) and thoracocentesis. PTX was diagnosed by the absence of the ‘glide sign,’ defined as the lack of the normal dynamic interface between lung margins gliding along the thoracic wall during respiration. Concurrent thoracic trauma was diagnosed by the presence of pleural or pericardial fluid or the presence of a ‘step sign,’ defined as an abnormal glide sign. Accuracy of TFAST was calculated relative to CXR findings.Results: Overall sensitivity (Se), specificity (Sp), and accuracy of TFAST relative to CXR were 78.1% (95% CI; 61.5, 89.9), 93.4% (95% CI; 87.4, 97.1), and 90.0%, respectively. Se and Sp were higher in dogs with penetrating trauma (93.3%, 96.0%) and for the evaluator with the most clinical experience (95.2%, 96.0%); only Se between the most experienced compared with others was statistically significant (P<0.05). TFAST documented other concurrent thoracic injury. Median time for TFAST was 3 minutes.Conclusions and Clinical Relevance: TFAST has the potential to rapidly diagnose PTX and other thoracic injury and guide therapy, including potentially life‐saving interventions, in traumatized dogs.

Background: Magnetic resonance imaging (MRI) is a correlate to physical examination in various myelopathies and a predictor of functional outcome. Objectives: To describe associations among MRI features, neurological dysfunction before MRI, and functional outcome in dogs with disk herniation. Animals: One hundred and fifty‐nine dogs with acute thoracolumbar disk herniation. Methods: Retrospective case series. Signalment, initial neurological function as assessed by a modified Frankel score (MFS), and ambulatory outcome at hospital discharge and >3 months (long‐term) follow‐up were recorded from medical records and telephone interview of owners. Associations were estimated between these parameters and MRI signal and morphometric data. Results: Dogs with intramedullary T2W hyperintensity had more severe pre‐MRI MFS (median 2, range 0–4) and lower ambulatory proportion at long‐term follow‐up (0.76) than those dogs lacking hyperintensity (median MFS 3, range 0–5; ambulatory proportion, 0.93) (P=.001 and .013, respectively). Each unit of T2W length ratio was associated with a 1.9 times lower odds of long‐term ambulation when adjusted for pre‐MRI MFS (95% confidence interval 1.0–3.52, P=.05). Dogs with a compressive length ratio >1.31 (which was the median ratio within this population) had more severe pre‐MRI MFS (median 3, range 0–5) compared with those with ratios ≤1.31 (median MFS 3, range 0–4; P=.006). Conclusions and Clinical Importance: MRI features were associated with initial injury severity in dogs with thoracolumbar disk herniation. Based on results of this study, the T2W length ratio and presence of T2W intramedullary hyperintensity appear to be predictive of long‐term ambulatory status.