My colleague Robert Allison finds the most interesting data sets to visualize! Yesterday he posted a visualization of toothless seniors in the US. More precisely, he created graphs that show the estimated prevalence of adults (65 years or older) who have had all their natural teeth extracted. The dental profession calls these people edentulous. According to the CDC, about 20% of seniors (more than 35 million Americans) are edentulous.

When I looked at his sorted bar chart, I noticed that the states that had the most toothless seniors seemed to be poorer states such as West Virginia, Kentucky, Tennessee, Mississippi, and Louisiana. In contrast, richer states such as Colorado, Connecticut, and Hawaii had a relatively small number of toothless seniors. I wondered whether there was a correlation between median income in a state and the number of edentulous individuals.

Rob always publishes his SAS programs, so I used his data and merged it with the state median household income (2-year-average medians) as reported by the US Census Bureau. Then I used the SGPLOT procedure to plot the incidence of toothlessness (with lower and upper confidence intervals) versus the median state incomes. I also added a loess curve as a visual smoother to the data, as follows:

```title "All Teeth Extracted vs. Median Income"; proc sgplot data=all; scatter x=income y=pct / yerrorlower=LCL yerrorupper=UCL datalabel=N; loess x=income y=pct; run;```

The resulting graph (click to enlarge) shows a strong linear correlation (ρ = -0.63) between the data, and the loess curve indicates that the relationship is stronger for states in which the median income is less than \$50,000. The confidence intervals indicate that most of the data is well approximated by the loess fit, but there are a few outliers.

Two states in the upper left corner of the graph (West Virginia and Kentucky) have incidences of edentulous that are much higher than suggested by the model that uses only median household income. Several states—including Montana, Florida, and Hawaii—have a much lower incidence of tooth extraction. For easy identification of the states on the scatter plot, you can create a second scatter plot that does not contain the confidence limits and instead displays the state names as labels.

Like Rob, I always post the full SAS code that creates the analyses and graphs in my blog posts, so feel free to play with the data and create more visualizations.

And regardless of your income or state of residence, brush your teeth!

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Distinguished Researcher in Computational Statistics

Rick Wicklin, PhD, is a distinguished researcher in computational statistics at SAS and is a principal developer of SAS/IML software. His areas of expertise include computational statistics, simulation, statistical graphics, and modern methods in statistical data analysis. Rick is author of the books Statistical Programming with SAS/IML Software and Simulating Data with SAS.

1. Robert Allison on

Nice analysis!

I wonder if Florida might be an anomaly because a lot of the 'rich' seniors from other states retire to Florida (and perhaps richer seniors have more money to take care of their teeth)? Just a theory! :)

2. Leonid Batkhan on

So the poorer people are more likely to lose all their teeth and the richer people somehow manage to keep them. Evidently, better health care takes more money, besides brushing your teeth.

3. Cecilia Hines on

As a dentist in Florida for 33 years and living in "lower Alabama" i.e. Northwest Florida which has more in common with the Deep South than the Northeast US, I'll make just a couple strictly empirical observations that can be classified as anecdotal at best. Rick can analyze any of these if he chooses to for statistical correlation.

First, I believe Robert Allison is right on about the Florida outlier/anomaly. Not so much here where many people still believe it is "normal" to have dentures after age 50 or so, in Central and South Florida there are many elderly who sell expensive homes in NJ or CT or wherever and retire. They frequently have pensions as well as social security and can afford higher end dentistry i.e. keeping their teeth. Frequently these transplants are also better educated than their southern counterparts as well.

Secondly, in this century there are a number of older people who are quite affluent and have some of their teeth but they are not in very good shape. Due to periodontal disease (FLOSS DAILY, MY FRIENDS!) the prognosis for these teeth following crowns and fixed bridges is not very good. Consequently, they opt to extract all their teeth (yes, they now are edentulous for your analysis) and have implants placed surgically which support and upper and lower denture but in a permanent fashion, unlike typical removable dentures. This treatment called all-on-four can run \$10,000 to \$45,000. So obviously this group would not be low income yet are edentulous. Just a fly in the ointment to throw in.

My final comment concerns what I see every week in the 3 free clinics where I volunteer. Patients as young as 30 come in with a mouthful of non-restorable teeth, many just roots broken off at the gumline. They are NOT edentulous but want to be because they are in so much pain. Some are homeless, some are former drug users, most are unemployed, none have any dental insurance. None of these clinics help with dentures but we will extract the hopeless teeth for free. Frequently it is obvious that the patient is neither brushing nor flossing. Priorities are often out of wack, i.e., they cannot afford to see a dentist but have smart phones, cigarettes, expensive nails or hair, name brand shoes. But how much does a toothbrush cost? When asked, they admit to rarely brushing! I cannot understand how these people were not educated by parents or teachers of the importance of oral hygiene in this day and age. But it is true. The other question I have is why the government (federal and state) do not consider teeth part of your body? Medicare covers zero dental and Medicaid in most states, especially the poorer ones, also has no or very limited provisions for dental care. An infected tooth can cause death yet it is not covered whereas an infected toe would be. Strange, but true.

Enough on my soapbox. Have a great day!

4. Edzard van Santen on

Another possible model might be a segmented linear model where above a certain median income there is no effect.