# 1.3 psychology statistics

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1.3 Psychology Statistics. AP Psychology Mr. Loomis. Descriptive Statistics. Definition… Describe a set of data Measures of Central Tendency Measures of Variation Skewed Distributions. Measures of Central Tendency. Mean Average score - PowerPoint PPT Presentation

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1.3 Psychology StatisticsAP PsychologyMr. LoomisDescriptive StatisticsDefinitionDescribe a set of data

Measures of Central TendencyMeasures of VariationSkewed DistributionsMeasures of Central TendencyMean Average scoreExtreme scores have a greater impact on the mean than on the mode or medianMedianScore that divides a frequency distribution exactly in half, so that the same number of scores lie on each side (middle)ModeMost frequently occurring score (bimodal)

Measures of VariationDefinitionMeasure of variation in a single score that presents info about the spread of scores in a variationRange highest minus the lowestStandard Deviation a standard measurement of how much the scores in a distribution deviate from the meanThe most widely used measure of variationZ-score (standard score) the distance of a score from the mean in units of standard deviation

Normal DistributionForm a bell-shaped or symmetrical curve

Normal DistributionThe percentage of scores that fall at or above the mean is 50the percentage that fall below (or at) the mean is also 50

Normal DistributionOn-third of the scores fall one standard deviation below the mean and on-third fall one standard deviation above the meanExampleWechsler IQ TestsMean = 100 / Standard Deviation = 15One-third score 85-100Another third score 100-115

68-95-99.7 Rule68% of scores fall within one SD 95% of scores fall within two SD99.7% of scores fall within three SD

PercentileDistance of a score from 0Examples90th percentile score better than 90%38th percentile score better than 38%

Skewed Distributions

Skewed DistributionsPositively Skewed DistributionsContain a preponderance of scores on the low end of the scale (looks like P lying on backMean is higher than the medianThus the median is a better representation of central tendency in positively skewed distributions

Skewed DistributionsNegatively Skewed DistributionsContain a preponderance of scores on the high end of the scaleMean is lower than medianThus the median is a better representation of central tendency in a negatively skewed distribution

Inferential StatisticsKey pointsMost experiments are conducted with a small sample of subjectsPsychologists want to generalize the results from their small sample to a larger populationIS are used to determine how likely it is that a studys outcome is due to chance and whether the outcome can be legitimately generalized to the larger population from the sample selected

The P-ValueProbability of concluding that a difference exists when in fact this difference does not existA statistically significant difference is a difference not likely due to chance (shows up 5% of the time or less)Smaller the p-value, the more significant the resultsCan never be 0 (researchers can never be 100% certain the results did not occur by chance)

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