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Jamil A. Malik (PhD) National Institute of Psychology Quaid-e-Azam Univeristy

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Categorical Binary variable: Only two categories Nominal variable: More than two categories Ordinal variable: Categories have a logical order Continuous (entities get a distinct score): Interval variable: Equal intervals on the variable represent equal differences Ratio variable: Ratios of scores on the scale must also make sense

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correlational or cross-sectional research where we observe what naturally goes on in the world without directly interfering with it experimental research where we manipulate one variable to see its effect on another Tertium quid (confounding variables): A third person or thing of indeterminate character Causality and Statistics

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Independent design Repeated measure design Systematic variation Unsystematic (Random) variation Randomization and counterbalancing

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Frequency distributions (histogram) Normal distribution (1)Skew: lack of symmetry (1)Positive (2)Negative (2)Kurtosis: pointyness (1)Leptokurtic (2)Platykurtic In a normal distribution the values of skew and kurtosis are 0

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The mode Most frequent The median The Middle The mean The average

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Range Difference of Largest and smallest Interquartile range Range of middle 50% Not affected by extreme scores Frequency distribution as probability distribution Normal distribution (z-score) ±1.96 (2.5% of extreem scores in a distribution) ±2.58 (1% of extreem scores in a distribution) ±3.29 (0.1% extreem scores in a distribution) Null hypothesis Alternate hypothesis

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Degree to which a statistical model represents the data Sample and population Real world models Statistical Models

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The mean Standard deviation and standard error Confidence intervals

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One- and two-tailed tests Type I and Type II errors Effect sizes (d, r, eta sq, odd ratios) r =.10 (small effect): In this case the effect explains 1% of the total variance. r =.30 (medium effect): The effect accounts for 9% of the total variance. r =.50 (large effect): The effect accounts for 25% of the variance. meta-analysis Statistical power

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