# Single case analyses

CogStat can handle comparisons when a single case (e.g., a patient) is compared to a group (e.g., a control group). The single-case hypothesis tests are based on the solution proposed by John R. Crawford and his colleagues.

At the moment, CogStat supports the following hypothesis tests:

- Compare the performance of a single case to a control group (i.e., the extremity of a task), as introduced in Crawford & Howell (1998).
- Compare the performance of a single case to a control group when the performance is measured as a slope (i.e., the extremity of a task expressed as a slope), as introduced in Crawford & Garthwaite (2004).

To perform other single-case hypothesis tests not supported by CogStat yet, you might use the single-case study statistic packages by John R Crawford.

## How to run a single-case analysis in CogStat?

**Preparing the data.** Load your data, where a grouping variable will tell whether a case is a single case or a member of the control group, and where there is a dependent variable. In a slope comparison analysis, you also need a slope standard error variable.

Your data should look like this:

Group | Dependent variable |
---|---|

nom | int |

Single case | 3 |

Control group | 3 |

Control group | 4 |

Control group | 2 |

Or if you compare slope data, your data should look like this:

Group | Slope | Slope SE |
---|---|---|

nom | int | int |

Single case | 3 | 0.2 |

Control group | 3 | 0.3 |

Control group | 4 | 0.4 |

Control group | 2 | 0.3 |

**Performing the analysis.** Then choose `Analysis > Compare groups`

, and set the appropriate grouping variable and dependent variable. To run a slope analysis, beyond setting the grouping variable and setting the slope values as the dependent variable, click on the `Single case slope...`

button, set the Slope SE variable, and set the number of trials per participant.

If the grouping variable includes two groups and one of the groups includes a single case (such as in the data sources above), the single-case hypothesis tests will be chosen automatically.

Note that the modified t-test will be run only if the control group is normally distributed.