Result Data Model

The output from {chef} is a data.table containing the statistics for each stratum within each endpoint based on the specified analysis data for each endpoint.

The columns in the table contain information on six different hierarchical levels, meaning that e.g. information on level 2 is a sub level of level 1.

The table utilizes a long format structure, ensuring that each row corresponds to the most granular level of information (level 6). This level comprises individual statistical outcomes derived from the applied statistical functions.

The six information levels in the output data from {chef} are:

1. Endpoint specification. This may entail multiple endpoint specifications within the output.
2. Endpoint. If a group_by argument is included in the endpoint specification, it will result in a set of endpoints for each group level within that specification. If group_by is absent, only a single endpoint will be generated.
3. Stratifier. These are applied to each endpoint. For instance, if the stratifiers are SEX and AGEGR, the endpoint will be divided into three entities (one for each stratifier, and an additional one for the total, which is a unique, fixed stratification with a singular stratum).
4. Statistical function. The R functions designated for application to each stratifier.
5. Stratum. The levels of each stratifier.
6. Statistics. The statistics corresponding to each stratum.

The table below describes all the columns in the output table. Note that information on levels 1-5 may be repeated on several rows, since level 6 is the defining row level.

Aggregation level	Column name	Type	Description
Level 1: Endpoint specification	endpoint_spec_id	int	Id of endpoint specification.
	study_metadata	list	Study metadata.
	pop_var	char	Population filter variable.
	pop_value	char	Population filter value.
	treatment_var	char	Treatment variable.
	treatment_refval	char	Treatment reference value.
	period_var	char	Period filter variable.
	period_value	char	Period filter value.
	custom_pop_filter	char	Custom (free text) population filter.
	endpoint_filter	char	Endpoint filter expression.
	group_by	list	List of variables to group by (cross combinations).
	stratify_by	list	List of variables on which to stratify the analysis data.
	key_analysis_data	char	Id of analysis data set (filtered by population filter).
Level 2: Endpoint	empty	logical	Indicates if the endpoint is empty (no events).
	endpoint_group_metadata	list	Specification of group slice.
	endpoint_group_filter	char	Filter expression to extract group slice from analysis data.
	endpoint_id	char	Endpoint id. One endpoint per group slice.
	endpoint_label	char	Endpoint label.
	event_index	list	Indices (rows) in the analysis data that are events.
	crit_accept_endpoint	logical	Evaluation of crit_endpoint.
Level 3: Stratifier	strata_var	char	Stratification variable.
	strata_id	char	Id of stratifier.
	crit_accept_by_strata_by_trt	logical	Evaluation of crit_by_strata_by_trt.
	crit_accept_by_strata_across_trt	logical	Evaluation of crit_by_strata_across_trt.
Level 4: Statistical function	fn_hash	char	Id of stat function.
	fn_type	char	Type of stat function (stat_by_strata_by_trt, stat_by_strata_across_trt, or stat_across_strata_across_trt).
	fn_name	char	Name of stat function.
	fn_call_char	char	Stat function parsing (name of stat function and arguments).
	fn_callable	list	Stat function code.
Level 5: Stratum	stat_empty	logical	Indicates if stratum is empty (cell_index is empty).
	stat_metadata	list	Specification of stratum.
	stat_filter	char	Filter expression to extract stratum from analysis data.
	stat_result_id	char	Id of statistics produced by stat function.
	cell_index	list	Indices (rows) in the analysis data included in the stratum.
Level 6: Statistics	stat_result_description	char	Description of the statistics (returned from statistical function).
	stat_result_label	char	Label to the statistics (returned from statistical function).
	stat_result_qualifiers	char	Qualifiers to the statistics (returned from statistical function).
	stat_result_value	num	The statistical value returned from the statistical function.