Description of column-types used to time-stamp data

TIME: data time stamp

The TIME columns define the time at wich dose and observation events occurred. When no DATE/DAT1/DAT2/DAT3 column is present, the time represents the time elapsed. When a DATE/DAT1/DAT2/DAT3 column is present, it represents the time of the day. The time can be defined using a double, or a clock format hh:mm or hh:mm:ss. Negative time values are allowed. When the double format is used, and no DATE/DAT1/DAT2/DAT3 column is present, the time has no predefined units. In all other cases, the time units are hours.

When a subject has time under the clock format, all times are converted into relative hours, as on the following example:

TIME Reconstructed time
10:00 10
10:30 10.5
14:00 14
08:59 8.983333

When there is no column-type TIME, the column-type NOMINAL TIME is used as time, and if neither TIME nor NOMINAL TIME column-types are present, the column-type DATE is ignored, and the first column-type REGRESSOR is used as time. If no columns are tagged as REGRESSOR, time will be equal to the index of row number containing observations / amounts for each subject-occasion.

Format restrictions

  • A data set shall not contain more than one column with the column-type TIME.
  • If the TIME column-type is used, the TIME must be defined for all lines.
  • String “.” will not be interpreted as a repetition of the previous line and is non-compliant with formats listed here-above.

NOMINAL TIME: data nominal time stamp

The NOMINAL TIME column defines the time at which doses and observations were expected to occur. The column format is the same as the format of the TIME column amd the same restrictions apply, with the exception that lines with missing values are not automatically ignored, but taken from TIME column, if it exists in the data set.

If defined, the NOMINAL TIME column:

  • can be used instead of TIME column on x-axis of Observed data (Monolix/PKanalix) and Visual predictive check (Monolix) plots,
  • can be used instead of TIME column in the NCA Concentrations table (PKanalix),
  • is used in NCA sparse data calculations (PKanalix),
  • is used in all other calculations, if TIME column is not defined (Monolix/PKanalix).

DATE/DAT1/DAT2/DAT3: date information

The DATE column-type can be used to indicate the date of the dose or observation event. It is usually used in combination with the TIME column-type, which in that case indicates the time of the day. To accommodate the different date formats, several column types are possible:

Format and associated date column name
Day, month and year mm/dd/yy or mm/dd/yyyy

mm-dd-yy or mm-dd-yyyy

dd/mm/yy or dd/mm/yyyy

dd-mm-yy or dd-mm-yyyy

yy/mm/dd or yyyy/mm/dd

yy-mm-dd or yyyy-mm-dd

yy/dd/mm or yyyy/dd/mm

yy-dd-mm or yyyy-dd-mm

By default, when the year is coded with two digits, it is interpreted as 20xx.

Format restrictions

  • A data set shall not contain more than one column-type DATE / DAT1 / DAT2 / DAT3.
  • Year, day, and month shall be integers.
  • The separator must be “/” or “-“
  • Character “.” will not be interpreted as a repetition of the previous line and is not compliant with the DATE formats.
  • All the lines should be filled correctly within the same delimiter, according to the specified date format: i.e., no empty year, no empty month, no empty day, no mix of delimiters.

Timestamp summary

There are several ways to define the timestamp of the data set depending if there is a TIME column or not and if there is a DATE column or not.  

(NOMINAL) TIME column present (NOMINAL) TIME column not present
DATE column present DATE column is considered to represent the day and the TIME column the hour within this day Date column ignored (regressor or index used)
DATE column not present TIME column is considered to represent the time (no specific units) First regression-column will be used to timestamp data


  • My data is not “over time”, what should I do? You can arbitrarily set the time of each observation to 0.
  • What happens if neither TIME nor DATE is defined? We strongly encourage the user to explicitly define the TIME column-type. However, if there is neither TIME nor DATE column-types, the first regression-column (i.e. first column with column-type REGRESSION) will be used to timestamp data. Moreover, if there is no TIME, no DATE and no REGRESSION column-type, time is equal to row indexes of each subject-occasion.