Descriptive Statistics

Descriptive Statistics • Number pictures of data • Number distributions • Measures of central tendency • Measures of variation • Z scores • Percent and percentile

Number Pictures • Frequency graph • Bar graph or histogram • Frequency polygon • Frequency curve

Frequency Graph

Bar Graph/Histogram

Frequency Polygon

Frequency Curve

Number Distributions • Normal curve • Negative skewed curve • Positive skewed curve

Normal Distribution -3 -2 -1 0 +1 +2 +3 Z

34.13% 34.13% 13.59% 13.59% 2.27% 2.27% 0 -3 -2 -1 +1 +2 +3 Z Normal Distribution

34.13% 34.13% 13.59% 13.59% 2.27% 2.27% 100 52 68 84 116 132 148 IQ TEST DISTRIBUTION Stanford-Binet

Mode Mean Median Negatively SkewedDistribution

Positively SkewedDistribution Mode Median Mean

Central Tendency • Mode • Median • Mean

Variation • Range • Variance • Standard deviation

Z Scores • Single score description • Relation of raw score to mean accounting for variation • Z = sum of • Standard score • Deviation score in standard deviation units

Percent • Proportion of a whole • Quantity - # units in proportion to 100 • %= (F)n / (t)n * 100

Percentile • A number’s position in a group of numbers • Percentage of numbers below the number • Median = 50th percentile

Descriptive Statistics