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Metrics and covariates are structures to organize non-timeseries and non-MRI measures. Examples include surveys, BP measures, and polysomnography scoring.

Covariates

A "covariate" is a stored value. The covariate has a name, and will be either a number or text ("string"). It will usually have a date (and possibly time) when it was measured.

The covariate information is stored in the "covariate" table. The actual values are stored separately as values in the "covariate_value" table.

Covariate table
Read only     
'covariate_id''int(11)''NO''PRI''''auto_increment'
'modified''timestamp''NO''''CURRENT_TIMESTAMP''on update CURRENT_TIMESTAMP'
Required     
'name''varchar(255)''NO'''''''
'valtype''enum(''number'',''string'')''YES'''''''
Optional     
'valdefault''varchar(255)''YES'''''''
'category''varchar(255)''YES'''''''
'description''varchar(4096)''YES'''''''
'parent_covariate_id''int(11)''YES'''''''
'formula''varchar(2048)''YES'''''''
Covariate_value table
Read only     
'covariate_value_id''int(11)''NO''PRI''''auto_increment'
'modified''timestamp''NO''''CURRENT_TIMESTAMP''on update CURRENT_TIMESTAMP'
Required     
'subject_id''int(11)''NO'''''''
'covariate_id''int(11)''NO'''''''
'value''varchar(255)''YES'''''''
Optional     
'name''varchar(255)''YES'''''''
'datetime''datetime''YES'''''''
'projectgroupstudy_id''int(11)''YES'''''''
'analysissetgroupstudy_id''int(11)''YES'''''''
'tag''varchar(1024)''YES'''''''
'comment''varchar(2048)''YES'''''''

Metrics

A metric is a way to group several covariates. For example, if you do a survey with several questionnaires, each questionnaire can be saved as a covariate value, but if you have a lot of questionnaires, it will become unwieldy. A metric could be "MRI visit survey" and consist of the questions and questionnaires asked on the day of the MRI visit. You can then link this to a study in a project. For example, to link polysomnography scores to a study with MRI's and physiology, create a new study "metric" and then in the project link that to the study, just like you link an MRI series or physiology recording. 

A "metric" is just a type of study associated with the subject, set in the subjects GUI. A separate very simple table records all covariate_values in that metric. 

Table metric
'study_id''int(11)''NO'
'covariate_value_id''int(11)''NO'

Note that one metric could have repeated entries - this might be useful to make up for missing data (I'm not sure).



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