This recoded variable is based on the following variables:

• CTCOLLNO: Time since last CT colonoscopy: units

• CTCOLLTP: Time since last CT colonoscopy: time period

• CTCOLLDMO: Calendar month of last CT colonoscopy

• CTCOLLDYR: Year of last CT colonoscopy

• CTCOLLESTY: Time since last CT colonoscopy: grouped year estimate

The 2010 and 2015 Cancer Layout files note that, "This is a time category recode for the time since the most recent CT colonography or virtual colonoscopy. All available information was used and the recoded variable was pre-filled with the response to the time category question first, if available. These data are provided by the respondent and are not imputed.

A similar variable, CTCOLLGYRR2, is a recoded variable that reports the time since the respondent's most recent CT colonography or virtual colonoscopy using the same method as the 2000 survey.