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CHAPTER 3.4
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3.4.3.5. Statistical analyses
The outcome variables analyzed were percentage TM and PM. To assess repeatability of
CASA and SQA-Ve (1.00.43) (experiment 1 only) each sample was analyzed twice within one minute.
First, it was tested whether the parameters changed over time (T1 vs. T2), using a paired-samples t-
test. Second, scatter plots were produced, where the value obtained at T1 was plotted against the
value obtained at T2. The line of perfect agreement (hatched line at 45° and intercept zero) was
integrated in each plot as comparison to the regression line to fit the data (Arunvipas et al., 2003).
Third, Bland and Altman plots were produced. This method plots the difference of the paired
measurements (y-axis) against their mean (x-axis) (Bland and Altman, 1986). Finally, for each
parameter, the coefficient of variation (CV) was calculated per sample and reported as mean CV over
all samples.
To assess agreement (experiment 1 and 2, respectively) observations obtained with CASA
were compared with these obtained with SQA-Ve. Statistical analysis was done as described for
repeatability using a paired samples t-test, scatter plots and Bland and Altman plots.
To be able to analyze all available observations, data reported by CASA were categorized
using the abovementioned SQA-Ve cut-off criteria (≤30% and >30%) and analyzed on contingency
tables using McNemar test (paired samples).
Statistical analysis was done using SPSS (version 17.0, SPSS Inc., Chicago, Illinois, USA).
3.4.4. Results
3.4.4.1. Experiment 1
For each of the different methods (CASA and SQA-Ve) 92 analyses were performed. This
yielded complete data for all observations using CASA. Analysis with SQA-Ve resulted in complete
data from 76 (82.6%) observations, incomplete data for 15 (16.3%) observations, and no data for 1
(1.1%) observation (Fig. 1). Complete data were available at T1 and T2 from 34 stallions and used for
further statistical analysis. Data were normally distributed. Averages did not differ significantly at T1
and T2 (Table 1). Analysis with CASA had mean CV’s