We received the following question about the postal code conversion file (PCCF) by email off-list and are sharing it with the dlilist as it may be of interest to other DLI contacts. Thank you.
"I have a question from a medical researcher regarding retired postal codes. Is it possible for individuals to continue using postal codes long after they have been retired? The researcher is working with hospital admitting data and is finding that approximately 6% of the patients' postal codes do not have a match in the corresponding PCCF; this is after the postal codes have been checked for errors. I have sent the researcher a copy of the auxilliary 2005 retired postal codes file which he will check against the missing ones.
Thank you in advance for any guidance you can provide with this question."
"The researcher will want to make sure that the vintage (postal code reference date) of the PCCF issue he/she is using matches the dataset (e.g. if the researcher is looking at individuals admitted in April 2007 and wants 2006 Census geography, the researcher will want to be using the April 2007 PCCF.)
The researcher can also check the retired postal code file to determine if the postal codes that don't have a match in the PCCF have been retired. Based on your message, I think that the researcher is already doing this.
When we asked our geography consultants to advise, they mentioned that "Postal codes do vary, with retirements and “re-births” occurring all the time.". They agreed with the suggestions above and also indicated that "It is important to know WHEN the postal code was recorded in the hospital records, it is possible that upon re-admittance at a later date, the postal code field may not be updated if the street address stayed the same (i.e. the nurse asks, “do you still live at 123 Anystreet in Anyplace, anyProvince”, if the answer is yes, they may not bother to ask, “is your postal code still ANA NAN?”)"
If there are still some issues with some specific postal codes after having checked that the correct issue of the PCCF is being used and that the codes haven't been retired, our geography consultants indicated that they could investigate those specific codes to see if there is anything they can find. I hope that these suggestions are helpful to the researcher. Please do not hesitate to let me know if you have any other questions."