This page lists the statistical fields that can be calculated and retrieved using Item analysis. Specify one or more of these fields when initialising your report dataset using Data API's SET /reports/datasets endpoint.

## Question Fields

These fields can be calculated for every Question in the dataset. Some fields are only available in a specific dataset type.

item_position |
The Item's position in the Activity. This will be empty unless the the Item is in the same position in all analyzed sessions. Only available in |
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item_reference | The reference of the Item that contains the Question. |

organisation_id |
The Item's source organization. This allows to disambiguate Items with the same reference found in multiple Item banks. |

question_number | The number of the Question within its Item. For example, the 2nd Question on an Item will have Question number `2` . |

question_reference | The reference of the Question. |

count_sessions |
The number of times this Question has appeared in a session. |

count_attempted | The number of times this Question has been attempted by a user. |

p_value | The average relative score of the Question, where relative score is defined as `score/max_score` . For unattempted Questions, a zero score is assumed. Ranges from `0` to `1` . |

stddev_p_value | Standard deviation of `p_value` . |

p_value_if_attempted | The average relative score of the Question, where relative score is defined as `score/max_score` . Unattempted Questions are not included in the calculation. Ranges from `0` to `1` |

stddev_p_value_if_attempted | Standard deviation of `p_value_if_attempted` . |

discrimination_index |
Measures how well a user's overall score correlates with their score on this Question. Ranges from Calculated by comparing the We first calculate the top and bottom 27th percentile of the overall Activity scores across the whole population. We then select users for the top group if their overall score is greater than or equal to the top 27th percentile score, using the same logic to select the bottom group. We then calculate the Only available in |

## Summary Fields

These summary fields result in a single value that applies to the whole dataset.

### ibk-analysis-by-question

count_questions |
The total number of Questions in the dataset. |
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### activity-analysis-by-question

count_questions |
The total number of Questions in the dataset. |
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count_sessions |
The total number of sessions matching the filters in the initial dataset request. |

count_sessions_analyzed |
The total number of sessions that contain exactly the same Questions, and were kept for analysis. |

count_sessions_discarded |
The total number of sessions that were discarded before analysis because they did not contain the correct set of Questions. |

count_sessions_top_27p |
The total number of sessions included in the top 27%, for the purposes of calculating |

count_sessions_bottom_27p |
The total number of sessions included in the bottom 27%, for the purposes of calculating |