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You can use the same format of protocol id for the metric as for MRI and physiology; because studies are selected by type, they will not get confused.
{noformat}[patient id][session number][yyyymmdd]
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Table metric
| 'study_id' | 'int(11)' | 'NO' |
| 'covariate_value_id' | 'int(11)' | 'NO' |
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