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# NU Research Methods

### Statistical Methods Flashcards 1

Question | Answer |
---|---|

range | length of the smallest interval which contains all the data |

interquartile range (IQR) | difference between the third and first quartiles |

Variance | amount of variation of all the scores for a variable s(square)=sum (x-mean(x))(square)/N |

Standard Deviation | square root of variance |

Normal Distribution | two-thirds of cases within one standard deviation of the mean two-thirds of cases within one standard deviation of the mean approximately 95% of cases within two standard deviations of the mean |

Deviation | x-x(mean) |

Experimental research design | a scientific control is used to minimize the unintended influence of other variables Random assignment of subjects |

Quasi-experimental design | Experimental method but without random assignment |

When is quasi experimental design used? | when randomization is impossible and/or impractical |

Advantages of quasi experimental design | Easier minimizes threats to external validity efficient in longitudinal research |

Disadvantages of quasi experimental design | Threats to internal validity Causal relationships difficult to determine Confounding variables |

Internal validity | extent to we can accurately state that the independent variable produced the observed effect |

Threats to internal validity | regression to the mean confounding variables extraneous variable occurring between pre- and post-measurement maturation instrumentation error investigator bias differential attrition |

External validity | Generalizability – to or across target populations – to or across tasks – to or across environments |

Threats to external validity | situation or environment Hawthorne effect (testing effect) Rosenthal effect Selection bias pre and post test effects |

Hawthorne effect | People act differently when they know they are being tested |

Non-experimental design | No control group Observational Used for theory development |

cross tabulation | A table of the frequency distribution of two or more variables |

Null hypothesis | hypothesis of no difference Something happens by chance or that no difference exists between populations |

Chi-square (χ2) | compares a set of frequencies expected if the null hypothesis is true (fe) against a set of frequencies observed in a sample (fo) |

Geometric mean | used for data based on ratios, proportionate growth, percentage change. |

differential attrition | extent of subjects who drop out of a study AKA mortality |

reliability | consistency of observations not the same as validity (could be consistently false) reliability is necessary BEFORE validity can be established |

Social desirability effect | Subject respond in a way that appears favorable to the tester |

Advantages of interviews | higher response rate more lengthy and detailed more complex more flexible linking |

Advantages of questionnaires | low cost protectivity (confidential) less reactivity |

reactivity | act of measuring changes responses |

Cohort study | Compare group of people who share a certain characteristic (smokers) with unexposed group(non-smokers). |

Experimental trial | Exposed v. unexposed groups in trial setting (drug v. placebo) |

Case control study | Historical, Subjects already have a condition, study looks back to see if there are characteristics of these patients that differ from those who don’t have the disease |

Odds Ratio | Probability that something will occur divided by probability it will not occur. |

Kurtosis | Measure of peakedness in frequency distributions |

platykurtic | lower, wider peak around the mean |

leptokurtic | a more acute peak around the mean (bunching toward the mean) |

skewness | a measure of the asymmetry of the probability distribution |

positive skew | Tail to the right is longer |

negative skew | Tail to the left is longer |

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