Psychological Statistics

# Psychological Statistics - Psychological Statistics S...

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Psychological Statistics: Statistics: a set of tools used to organize, describe, and analyze numerical observations. Descriptive: describe. Inferential: infer to analyze. Parameters is to population as statistic is to sample. Discrepancy between population and sample mean(s) is sampling error. Data is the collection of numerical observations from a survey or experiment; single is datum: raw score. Qualitative: observation of class/category; categorical data. Quantitative: amount or count. Discrete: countable # of possible values. Continuous: infinite # of possible. Variables can change (X/Y etc.) and usually do; then measured. Constants remain just that. IV (independent variable): manipulated variable. DV (dependent variable); variable that is measured; effect. Correlational studies compare 2 DVs for relationship. Nominal: category, label. Ordinal: name + order. Interval: name + order + distance (standard). Ratio: all + distance from 0. Quasi-independent variable(nonexperimental method), Real limits, Construct, Operational definition, Summation Descriptive Statistics: Frequency distribution: collected observations showing the # of times each observation occurs. Grouped: for large # of values. Ungrouped: smaller manageable data. Outliers: extreme values in a distribution. 3 X 3: Histograms (bar), frequency polygon (line), bar graphs (discrete); normal, bimodal, skewed (pos./neg.). Measure of central tendency: where center of distribution is located. Mode: most frequently occurring score (often for qualitative data). Median: point that divides top 50% from bottom, skewed distribution(s) (# of scores + ½). Mean: arithmetic average of scores (sum/# of scores), see-saw. Weighted mean, characteristics of the mean, fine-tuned median for continuous variables, when to use median. Range: variability measure; distance from lowest to highest score: (Highest-lowest) + 1, observations increase, range increases; increased probability of extreme values. IQR (interquartile range): # of observations + 1/4; find scores add and divide by 2 range of middle 50% of observations, not sensitive to extreme values. Variance: sum of squared

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deviations (SS) about the mean (divided by n/N). Standard deviation: square root of variance. Bias: inaccurate picture of pop. by sample; n-1 helps correct for bias. Normal density curve: Symmetrical, bell-shaped, unimodal, mean=median=mode, probability density plot (has equation; uplook). Standard normal curve: always have a mean of 0, and a standard deviation of 1, and scores are z/standard scores. Z Score(s): difference of
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