Date/time data is a special case of interval data
- A specific time or day and time has been specified as 0.
- The value can be used to work out the time since the 0 time.
The table below shows how dates and times are recorded in different data analysis software.
Number of seconds since 14 October 1582 (i.e., a 1 indicates the 1st second of the 14th of October 1582).
Number of milliseconds since 1 January 1970. For example:
The number of days since the 0th of January 1900. For example, a 1 indicates the 1st of January 1900.
Unlike interval data in general, software that can understand Date/Time data can be used to easily perform certain types of time-based analysis, such as:
- Calculating differences between times in different time points, such as days, weeks, months, and years. Note that this is not as trivial as it sounds, as the presence of leap years and related anomalies mean that simple calculations performed on Date/Time data can be misleading.
Some software will automatically convert Date/Time data to some other format when conducting analysis. For example, Q and Displayr automatically aggregate the data into bands when using the data as an input to a table.