TDWI | Training & Research | Business Intelligence, Analytics, Big Data, Data Warehousing

Data: Keep It Fundamental and Stable

When deciding what data elements to store, consider the difference between your birth date and your age.

• By Mike Schiff
• November 20, 2018

I was recently at a doctor's office where I was asked to fill out a series of forms with space for the current date as well as my date of birth and my age. Since my age is a function of the current date minus my date of birth, I considered the age question to be somewhat redundant. Furthermore, although my birth date does not change and is thus a stable piece of data, my age is transitory as it continues to increase as time goes by.

For Further Reading: Timely Information: How Current Is This? Achieving Customer Intimacy with Complete Data Reducing the Impact of Bad Data on Your Business

This reminded me of a time when many years (decades!) ago I was asked to describe the difference between data and information. I chose not to dwell on how processing data yields information that can then be used to provide knowledge or initiate actions. Instead, I provided the simplest example I could quickly think of: I considered someone's birth date to be fundamental data and that person's age to be information. In fact, I joked that if your employee master file stored age rather than birth date, you should be prepared to increment every employee's age by one on their birthdays (which in this scenario was probably not in the master file).

I am strongly recommending storing a person's date of birth rather than their age, but there are certainly times when age would be appropriate. For example, in healthcare analysis, many studies look at medical histories to track and correlate the onset of symptoms with age. Consequently, the current date less the birth date would not be correct.

However, although the observation date less the birth date would yield the age, privacy concerns including data anonymity may preclude storing someone's birth date because it might be used along with other data to identify the person. In this situation, storing the age at time of observation might be more appropriate.

Capturing birth date rather than age applies not only to people and other living things such as animals or plants, but to other data subjects as well, such as accounts receivable (where invoice date should be stored rather than how old the invoice is), product manufacturer date (to determine shelf life or expiration date), or even real estate listing date (to determine the listing's age or days on the market). In fact, on almost all printed real estate listings, the days-on-market figure is higher than stated by the time you receive it.

The Bottom Line

When considering what to store in your data warehouse, favor stable fundamental data such as date of birth rather than transient information such as age. If only age is stored, make sure you also store the observation or "as of" date as well.