precision of STP measured using an optical refractometer and IgG concentration measured using RID in neonatal calf serum by evaluating the amount of variance produced by each test. We hypothesized that STP measured using an optical refractometer would
locomotion have been correlated with observed lameness and altered PVF and VI. 4–6
Limiting variance improves data quality and aids in interpretation of gait analysis results. Variance in GRF values can be affected by dog body weight and conformation
population of dogs in which SI may be unreliable, GRF data need to be normalized to account for the variation among individual dogs to minimize variance when groups of dogs are compared. It is common to normalize GRF data on the basis of body weight, but this
Procedure—Results of dynamic portoscintigraphic
studies were reviewed by 4 radiologists without
knowledge of signalment, history, or medical profile.
Results were judged to be negative or positive on the
basis of the dynamic scan. Composite images were
formulated, and hand-drawn regions of interest were
determined for the heart and liver. Time-activity
curves were generated, time-zero points were selected,
curves were integrated during a 10-second interval,
and shunt fractions were calculated.
Results—Radiologists were in agreement regarding
positive versus negative results for 99 of 101 studies.
Interoperator variance in shunt fraction calculation
ranged from 0.4 to 59.6%. For 51 studies with positive
results, variance ranged from 2.5 to 59.6% (mean
± SD, 22.8 ± 14.5%); differences among reviewers
were significant. For 48 studies with negative results,
variance in shunt fraction ranged from 0.4 to 25.9%
(mean, 5.3 ± 5.8%); significant differences among
reviewers were not detected. Shunt fraction calculations
were not exactly reproducible among radiologists
in 94 and 100% of studies with negative or positive
Conclusions and Clinical Relevance—Results suggest
that shunt fraction values are not reproducible
among operators. Range in variability was greater in
studies with positive results. This factor may be of
particular clinical importance in reassessment of
patients after incomplete shunt ligation. (J Am Vet
Med Assoc 2001;218:1116–1119)
influence GRFs. 7–11 Normalization of GRFs to body weight and the use of narrow velocity ranges (± 0.3 m/s) with controlled acceleration (± 0.5 m/s 2 ) have been recommended to minimize data variance, as determined on the basis of studies 9,10,12 in small
interpretive criteria for humans.
Data analysis —Statistical software e was used to perform all statistical analyses, including descriptive statistics. A nested ANOVA was used to analyze field data to determine the composition of the variance for 3 (isolate
contribution of each repeated measure to data variance was calculated. Results were considered significant at P < 0.05.
Of the 27 horses included in the study, 13 were geldings and 14 were mares. Horses ranged from 5 to 31 years of age (mean
prospective study reported here was to compare the within-subject variance for CO in healthy anesthetized adult horses when measured by 4 thermodilution protocols (injection of physiologic saline solution chilled to < 5 °C at volumes of 1 mL/15 kg, 1 mL/25 kg
scan was considered a separate event for this analysis. For evaluation of within-patient variance, dogs with multiple CT scans were included only when the same positioning for each CT event was used.
Results for the LEP were
observer (FCS), who was unaware of results from previous measurement trials. Intraobserver variability was determined via calculation of the coefficient of variance determined for 6 measurements for each variable measured in CT images of 1 dog with hind