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