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# PS2024

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Term | Definition |
---|---|

systematic source of variability/systematic variance | variance due to the manipulations we have introduced in the study (in other words those that are under our control, our effects) |

unsystematic source of variability/unsystematic variance | error variance; due to chance factors which are typically out of our control and which have not been varied systematically across participants in the study. |

t-test | statistical test for comparing two different means |

ANOVA/analysis of variance | statistical test allowing comparison of more than two different means |

within group variation | = experimental error; assumed the same between all groups individual differences/experimenter error/chance factors |

between group variation | why means differ across groups condition effects + experimental error |

F ratio | between group variation / within group variation = 1 if no condition effects > 1 if condition effects |

type 1 error | rejecting the null hypothesis where it should have been accepted defined by α-level |

α-level | the probability level on which the decision to accept the null hypothesis is based (usually p > 0.05) |

effect size | family of indices giving us information about the strength of effect(s) allows: assessment of treatment magnitude (IV on DV) comparison of effects with other studies aggregation of results for meta analysis estimation of required sample size |

eta-squared (η²) | η² = SSeffect/SStotal proportion of total DV variance attributed to an effect closer to 1 = larger effect |

partial eta-squared (partial η²) | ηp² = SSeffect/(SSeffect + SSerror) less biased than η² (takes less of design into account) |

ω2 | measure of effect size estimate of how much variance in the DV is accounted for by the IVs less biased alternative to eta-squared, especially when sample sizes are small. ω2 = (SSeffect – (dfeffect)(MSerror)) / (MSerror + SStotal) |

ωp2 | ωp2 = (SSeffect – (dfeffect)(MSs/Cells)) / (SSeffect + (N - dfeffect)MSs/Cells) |