3 Comments on materials and method
3.8 Statistical analysis
3.8.1 Project I
The results were presented as mean ± SD. For each time point in each horse, delta cortisol concentration was calculated as cortisol concentration measured at that time minus the baseline cortisol concentration. Differences in endogenous cortisol and ACTH concentrations, ACTH-stimulated cortisol concentrations, delta cortisol concentrations, and CBC results over time were analysed by means of repeated-measures ANOVA followed by the least significant difference test. Analyses were performed with standard software. (SAS software, version 9.1, SAS Institute Inc, Cary, NC.) The dose effect at each time point was determined by comparison of the ACTH-stimulated cortisol concentration with the cortisol concentration measured after administration of saline solution. The cortisol concentration measured at each time point, for each cosyntropin dose, was
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compared with the baseline cortisol concentration. Baseline endogenous serum cortisol and plasma ACTH concentrations were also compared among days that samples were collected. Differences in maximum cortisol concentration and time of maximum cortisol concentration between doses were determined by using the Friedman repeated-measures test, with post hoc comparisons performed using the Student-Newman-Keuls method (SigmaStat for Windows, version 1.0, Jandel Scientific, SPSS Inc, Chicago, Ill.) For all analyses, values of P < 0.05 were considered significant.
3.8.2 Project II
Results are summarized as mean ± SD values. For each time point after baseline for each foal, delta cortisol concentration was calculated as cortisol concentration measured at that time minus the baseline cortisol concentration. Differences in ACTH-stimulated cortisol concentrations, delta cortisol concentrations, and CBC results were analyzed via the mixed model for 2-D (time and dose) repeated-measures ANOVA and the Scheffe test for multiple comparisons. Analyses were performed with standard software (SAS software, version 9.1, SAS Institute Inc, Cary, NC.). The dose effect at each time point was determined by comparing the ACTH-stimulated cortisol concentration with the cortisol concentration measured after administration of saline solution. For each cosyntropin dose, cortisol concentration measured at each time point was compared with the baseline concentration. Baseline endogenous serum cortisol and plasma ACTH concentrations were also compared among days that samples were collected. Differences in maximum cortisol concentration and time of maximum cortisol concentration between doses were determined. For all analyses, values of P < 0.05 were considered significant.
3.8.3 Project III
Horses were categorized based on survival, hyperinsulinemia, hyperglycaemia and number of SIRS criteria and compared with P < 0.05 considered statistically significant. Normality was assessed by a Shapiro-Wilk normality test. Data following normal distribution were reported as mean ± SD and compared with an unpaired t-test, whereas data not following a normal distribution were reported as median [range] and compared using a Mann-Whitney U-test. A receiver operating characteristic (ROC) curve was plotted to analyse the prognostic value of a given variable (serum insulin, serum glucose or ratios). When more than 2 groups were compared, an ANOVA was used for normally distributed data and a Kruskal-Wallis test was used for non-normally distributed
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data with a Dunn’s post hoc test when appropriate. Categorical data were reported as counts and percentage of horses in which the variable was documented and compared using either a Chi-square test or a Fisher’s exact test depending on expected counts. Odds ratios and 95% confidence intervals were calculated when appropriate. Statistical analysis was performed using commercially available statistical software (Prism, GraphPad Software, Inc. La Jolla, CA 92037, USA).
3.8.4 Project IV
Horses were categorized based on survival (discharged alive or not), presence of SIRS (≥ 2 SIRS criteria), number of SIRS criteria (SIRS score) and presence of an ischemic gastrointestinal lesion and compared, with P < .05 considered statistically significant. Normality was assessed by a Shapiro-Wilk normality test. A receiver operating characteristic (ROC) curve was plotted to analyse the prognostic value of a given variable (ACTH, cortisol or ACTH/cortisol ratio) at admission for predicting survival, presence of an ischemic lesion or SIRS. A two-way repeated measures ANOVA was used to determine the effect of survival, SIRS or ischemia and time and Sidak’s multiple comparisons test was used for post hoc analysis. Data following a normal distribution were reported as mean ± SD values and data not following a normal distribution were reported as median [range]. Categorical data were reported as counts and percentage of horses in which the variable was documented and compared using either a Chi- square test or a Fisher’s exact test depending on expected counts. Odds ratios (OR) and 95% confidence intervals were calculated when appropriate. Any groups with low numbers of data were excluded from statistical analysis. Commercially available statistical software was used (Prism, GraphPad Software, Inc. La Jolla, CA 92037, USA).
3.8.5 Project IV
The statistical analysis was identical to project IV except for the following: For admission data, data following normal distribution were compared with an unpaired t-test or a one-way ANOVA, depending on the number of groups compared, whereas data not following a normal distribution were compared using a Mann-Whitney U-test or a Kruskal-Wallis test, depending on the number of groups compared. To compare data during hospitalisation, a two-way repeated measures ANOVA was used to determine the effect of outcome of interest (survival, SIRS and ischemia) and time using data from horses that had a complete set of data.
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This section summarizes the main results from the separate studies. More detailed descriptions are presented in each of the papers (I –V). Figures and tables referred to the respective published papers and manuscripts are located at the end of the thesis