# Lecture 7 - Quick review of parametric assumptions In order...

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1 Quick review of parametric assumptions In order to use parametric statistics your data must comply with certain assumptions

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2 Parametric assumptions • Data must be of interval quality or better – Creates ambiguity with Likert scale - if data are normally distributed use parametric test • Normality - Data must be normally distributed. Determined through: – Histogram with large samples can give indication - remains subjective Kolmogorov- Smirnov test - If the p value is statistically significant assumption of normality is unsafe to make
3 Parametric assumptions Kurtosis - measures peaked ness -ve indicates too many cases in the tails of the distribution, +ve indicates too few cases in the tails. Assume normality if in range of ±2 Skewness - extent to which data are overly bunched in one tail only. Negative skew is right-leaning, positive skew left-leaning. Assume normality if in range of ±2

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4 • Homogenity of variance - the variance between groups must be ‘equivalent’ – Formal test when using a between groups test is the Levene’s test. If p is significant then need to change formula slightly or use nonparametric • Independence of observations - performance of one participant should not influence that of another Parametric assumptions
5 Analysing frequency data Inferential statistics for nominal data - Chi-square ( χ 2 )

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6 Options for nominal data • Nominal data involves categories only • If we have an IV which has two levels, both of nominal quality, then we would have an expectation as to how many of each category would be present e.g., males and
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Lecture 7 - Quick review of parametric assumptions In order...

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