This topic answers some common questions about visits and timepoints.
How Do I Set Up Per-Participant Start Dates?
In date-based studies you can override the generic start date, instead using a participant-specific start date, which will be used to calculate visit positions, time-related reports, and all other alignments in the study, relative to the individualized start dates. To set participant-specific start dates:
- Add a column named "StartDate" to a demographic dataset. Do not replace or rename the Date column, as it is still a required column in date-based datasets. Retain the Date column and add StartDate as an additional column. For example:
Example Demographics Dataset with StartDate
Why Have Visits Been Created That I Did Not Pre-define?
Visits can be created manually (see Create Visits Manually
) or automatically when data is imported. When demographic, clinical, or assay data is imported into the study, the server will create new visits for the data if those visits have not already been pre-defined. For example, suppose that three visits have already been manually defined in a study having the VisitIds "1", "2", and "3". When the following dataset is imported into the study, the server will load three of the records into the pre-existing visits and it will automatically create a fourth visit to hold the last row of data.
How Do I Fix Negative Timepoints?
In a date-based study, negative timepoints indicate that some records in the datasets possess dates that precede the generic start date for the study. To get rid of the negative timepoints, do the following:
- Find the earliest date referred to in the datasets. Visit each likely dataset, and examine the Date field using "sort ascending" to find the earliest date in that dataset.
- Use this earliest record data in the study as the generic start date for the study. To reset the generic start date, see Study Properties.
- Recalculate the timepoints relative to the new generic start date. (See Manage Visits or Timepoints.)
- Delete any empty visits that result from the recalculation. (See Manage Visits or Timepoints.)
How are Visits and Timepoints Created?
Visits and Timepoints can be created in the following ways:
- Manually by explicitly defining them before any data is imported to the study.
- Automatically by importing data with new dates or visit numbers embedded in the data. When the server parses new incoming dataset records, new timepoints/visits will be created for any new dates/visit numbers it finds in the data.
Can a Visit-based Study be Converted to a Date-based Study? Or Vice Versa?
Generally, the date-based/visit-based choice is a permanent choice. You can switch types at the time of study creation before data is imported, but after data is imported, you can make only limited changes.
- "Visit" studies with data cannot be converted to "Date" or "Continuous" studies.
- "Date" and "Continuous" timepoint studies can be toggled back and forth with some caveats.
If you find you need to change to or from the "Visit" study type, you could recreate the study in a new study folder, recasting it in a different time-style. Create a new study, choosing the desired timepoint type, and re-import the datasets.
What is the Role of the Generic StartDate Field in Visit-based Studies?
Visit-based studies, which use decimal numbers to indicate visits and time sequences in the study, still allow you to specific a "Start Date" for the study. This date is available purely as "metadata" for the study, but is not used in any of the time-related calculations in the study.