Is Age An Interval Variable

In statistics, all variables are measured on one of four measurement scales:

Nominal: Variables that have no quantitative values.
Ordinal: Variables that have a natural order, only no quantifiable deviation between values.
Interval: Variables that have a natural order and a quantifiable departure between values, but no "true zero" value.
Ratio: Variables that have a natural order, a quantifiable difference between values, and a "true nothing" value.

The following graphic summarizes these different levels of measurement:

One question students oftentimes take is:

Is "age" considered an interval or ratio variable?

The short answer:

Age is considered a ratio variable because it has a "true zero" value.

Information technology's possible for an individual to exist cipher years onetime (a newborn) and we can say that the divergence between 0 years and 10 years is the same equally the difference between 10 years and 20 years.

Since age is a ratio variable, nosotros can also say that someone who is ten years old is twice as erstwhile as someone who is 5 years one-time.

Dissimilarity this with an interval variable like temperature: Nosotros cannot say that 10 degrees Celsius is twice equally warm equally five degrees Celsius because there is no "true zero" when it comes to temperature since degrees can exist negative.

When is Historic period Not a Ratio Variable?

The simply time that historic period would not exist considered a ratio variable is if the data we collect on historic period is in categories.

For instance, we may send out a survey and ask people to report which historic period bracket they vest in from the following choices:

0-nineteen years quondam
twenty-39 years former
xl-59 years old
lx+ years old

In this scenario, age would be treated as an ordinal variable considering a natural order exists among the potential values.

Nosotros would say 0-19 years old is younger than 20-39 years old, which is younger than 40-50 years old, which is younger than 60+ years onetime.

We would not allocate historic period as a ratio variable in this scenario considering we can't say with certainty that someone in the 20-39 years former group is twice as old as someone in the 0-xix years age group since we don't know exact ages.

This represents a rare scenario where we would not classify age as a ratio variable.

Boosted Resource

Levels of Measurement: Nominal, Ordinal, Interval and Ratio
Is Age a Discrete or Continuous Variable?
Categorical vs. Quantitative Variables