The psychopathology of everyday art: a quantitative Study - World ...

findings are unreliable because cases were mostly removed from one group: 6 cases from
the control group, 2 from group 5 and one from group 3, so purple was dropped.
There were 2 further variables, Orange and Black ((table/fig 2a and 2b, appendix
2), which showed significant heterogeneity in the groups. Transformation of the data did
not produce appreciable difference and the removal of outliers did not affect the
distribution. Therefore no clear appropriate transformation of these figures emerged.
The assumption that the groups came from populations with the same variance is
important: the standard differences from the mean of each variable by group was plotted
(Plots 6a-m and 7a-c, appendix 2). The plot for Orange (7a) clearly shows that diagnostic
groups 1 and 4 have a much wider scatter of differences than the others and there are
cases concentrated below the mean. The plot for Black (6f) shows only one group
(controls) with wide variance and no concentrations of cases. The results of the
Bartletts-Box Homogeneity of Variance Test 286 (table 8 below) showed the range was
unacceptable for Orange and it was dropped from the analysis, but was within tolerance
for the ANOVA for Black which was retained.
Normality of the final distribution
There were 12 remaining variables (tables/figures 2a-f and 3a-f, appendix 2 show mean
values, standard deviations and standard error of the mean (how much the sample means
vary in repeated samples from the same population)). Most of the standard errors were
286
Bartletts test is an extension of the F test for assessing the null hypothesis that more than two samples
come from populations with the same variance, recommended with ANOVA: P. Armitage and G. Berry
(1987), Statistical Methods in Medical Research , Oxford: Blackwell, p.209.
245