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Median, Not Average, Ages Across the County

I need to begin this issue’s column with the acknowledgement of an error I made a few weeks ago. In my column that discussed the reported median age of my hometown, Sister Bay, I inadvertently used the terms “median” and “average” as though they were interchangeable. They are not interchangeable as many of my erudite readers were quick to point out. So allow me to take a moment to clear up any confusion that might exist about the term “median.”

When it comes to “averages” the general populace is most familiar with what mathematicians call the “mean average.” This average is calculated by adding up all the numbers within a set of numbers and dividing the sum by the number of numbers within the set. Let’s say we have a set of numbers that include 19, 15, 15, and 7. When you total these four numbers together the result is 56. And if you divide that result by the number of numbers in the set (i.e. 4) you get a “mean average” of 14.

A “median” is calculated by determining the exact middle of a set of number. In other words, there are an equal number of numbers above and below “median average.” So in our example above, the “median” is 15.

Not surprisingly, many of those that contacted me about my error hoped that when I said “median” in my column about Sister Bay I actually meant “mean average.” Unfortunately, the Census always reports the median age for a community. Thus, when I stated that Sister Bay had a median age of 62.7 years-of-age in the 2010 Census, it meant that half the village’s residents were over the age of 62.7 and half were under the age of 62.7.

Also at the request of many of you, I put together a table showing the population and median age for the rest of Door County, showing the data from both the 2000 and the 2010 Censuses. Because of its size, I won’t have much more to say about it this issue, so I encourage you to save this table for reference. There are, however, a few points of explanation that I need to point out.

I used the communities that are members of the Tourism Zone Commission in the table. I do want to point out that, if you total the population columns they do not match the county’s total population as reported by the Census for either 2000 or 2010. They are not off by much, but they are off. At this point, I am not certain why, but I have some theories I am researching.

You will note that I placed an asterisk in both the population and median age columns for Baileys Harbor in the 2010 Census portion. The reason is that the Census in 2010 breaks the data into two portions: the Town of Baileys Harbor and “Baileys Harbor CDP.” According to the Census glossary, a CDP is:

A statistical entity, defined for each decennial census according to Census Bureau guidelines, comprising a densely settled concentration of population that is not within an incorporated place, but is locally identified by a name. CDPs are delineated cooperatively by state and local officials and the Census Bureau, following Census Bureau guidelines. Beginning with Census 2000 there are no size limits.

With this understood, the 2010 Census reports that the Town of Baileys Harbor had a population of 1022 with a median age of 54.8. The Baileys Harbor CDP has a population of 257 with a median age of 56.6.

* See explanation on Baileys Harbor’s 2010 Census numbers in the article.

Feel free to email me with questions about the data above, and I will try to answer each one either personally or in a future column.