Sweating the Small Stuff: Does data cleaning and testing ... - Frontiers

Kasper and ÜnlüAssumptions of factor analytic approaches0.2 0.4 0.6 0.8number of extracted factors109876543210987654321098765432PLPCSTPCKGPC0.2 0.4 0.6 0.8PLEASTEAKGEArelative frequencyPLPASTPAKGPA0.2 0.4 0.6 0.8Normal Slightly skewed Strongly skewedFIGURE 2 | Relative frequencies of the numbers of extracted factors, for n = 200 and k = 4. Factor models are principal component analysis (PCA, or PC),exploratory factor analysis (EFA, or EA), and principal axis analysis (PAA, or PA). Kaiser-Guttman criterion (KG), scree test (ST), and parallel analysis (PL) serve asfactor extraction criteria.words, strongly negative skewed distributions may not be estimatedwithout bias based on the classical factor models. Increasingsample size, for example from n = 200 to 600, or changing thenumber of underlying factors, say from k = 4 to 8, did not alterthis observation considerably. For that reason, the correspondingplots at this point of the paper are omitted and can be found inKasper (2012).We performed Shapiro-Wilk tests for univariate normality ofthe estimated factor scores. As can be seen from Figure 7A, undernormally distributed true latent ability scores nearly all values of Ware statistically non-significant. In these cases, the null hypothesiscannot be rejected.A similar conclusion can be drawn when the true latent abilityvalues are not normally distributed but instead follow a slightlyskewed distribution (Figure 7B). Nearly all Shapiro-Wilk test statisticvalues are statistically non-significant. In other words, thenull hypothesis stating normally distributed latent ability valuesis seldom rejected although the true latent distribution is skewedand not normal. No relationship between the p-values and the usedfactor model or factor position may be apparent (disregarding theobservation that the p-values for the fourth factor are generallylower than for the other factors).The case of a strongly skewed factor score distribution isdepicted in Figure 7C. Virtually all values of W are statisticallysignificant and the null hypothesis of normality of factor scoresis rejected. Similar conclusions or observations may be drawn forincreased sample size or factor space dimension and we do omitpresenting plots thereof.Finally, Figure 8 shows the distribution of the estimated factorscores on the fourth factor (for k = 4) in comparison to the truestrongly skewed ability distribution under the exploratory factoranalysis model for a sample size of n = 1,000. The unit normaldistribution is plotted as a reference. The estimated factor scoreshave a skewness value of −0.47 compared to true skewness −2.The estimated distribution deviates from the true distribution anddoes not approximate it acceptably well.Frontiers in Psychology | Quantitative Psychology and Measurement March 2013 | Volume 4 | Article 109 | 131