Statistics

Statistics

• descriptive statistics: ways to describe larger amounts of data (graphs, tables)

• inferential statistics: generalizing beyond experimental measures

• population: all individuals of interest to a study

• sample: a representative set of individuals from pop.

• random sampling + random assignment

• observational studies

  • compare 2 variables to determine if a relationship exists

  • does not prove causation

  • not manipulated by experimenter

• confounding variables

• experimental studies

  • independent variable: experimenter changes

  • dependent variable: experimenter measures

• histograms

  • positive skew (to the left)

  • negative skew (to the right)

  • normal

• central tendencies: central point of distribution

  • mean

  • use median if distribution is skewed / has outliers

  • use mode when describing shape of distribution

• variability: how scattered the scores are around the central point

  • range

  • interquartile range

  • standard deviation

    • mean, find distance from mean, square it

    • multiplying by a constant will multiple sd by that constant

  • variance: sd^2

• SS: sum of squared deviations

• degrees of freedom: number of scores free to vary

  • sample variance: ss / n-1

  • population variance: ss / n