If you pay attention to either science or woo journalism surrounding medicine and health, you’ve probably come across someone using a statistic regarding yearly diagnosing rates of various disorders.
One well-known example is the statistic bandied about by anti-vaxxers: that the rate of autism diagnoses have risen since the implementation of regular childhood vaccinations. This is used as proof that vaccines must cause autism. The same thing however can be said for the number of cars per household in the United States. By this logic, owning vehicles can cause autism.
Similarly, a recent article discussing a potential crohn’s vaccine discussed the rising rates of crohn’s diagnoses as proof that the condition was linked to a bacteria found in cattle. Interestingly enough the same statistic is used as proof for the theory that crohn’s is caused by historical poverty leading to a need for higher immune systems which are overpowered for our more sterile society.
Increased number of diagnoses in the last severalyears have been used to discredit the existence of depression, anxiety, ADHD, and many other mental health issues. As proof of an overmedicating society.
The idea of increased rates of diagnoses as a basis of proof falls into the old skeptical trope: correlation is not causation.
While it is true that one might be able to show an increasing rate of diagnoses over time, that statistic fails to ignore many important factors that can impact that rate.
In the case of anti-vaxxers and autism, it ignores that the diagnostic criteria for autism have changed over the years, while screening methods have dramatically improved. For example the DSM-V eliminated Asperger’s as a diagnosis and brought it under the general autism diagnosis. This would make it appear that there were suddenly a greater number of autistic people when in fact the number is the same, it’s just the label that changed.
This is also true of ADHD, as more and more schools know what to look out for, and more and more people become aware of the diagnostic criteria for girls.
In the case of both of these, it ignores how diagnoses have increased significantly among white males, more than among girls and people of colour. It ignored how the rate of diagnosis also correlates with access to mental health care, insurance, and with the number of programs aimed at identifying children in the schools themselves.
Similarly, the Crohn’s article completely ignores that there have been dramatic improvements in the imaging technology that’s available to doctors. This grants them a clearer picture of what is going on internally and allows them to reach the correct diagnosis. The last several years have also meant more visibility for crohn’s and colitis, making more doctors aware of what to look for. This means that a patient has a greater chance of being referred to the right specialist to receive said diagnosis.
The actual disease known as Crohn’s has only been established since about 1932, so any statistics claiming an increase of diagnoses in the last 100 years ignores that for the first 16 years it didn’t exist as a diagnosis. As our knowledge of the disorder grew, so did our ability to actively identify it. Even now, colonoscopies are only successful in identifying the disease in 70% of cases.
Rates of diagnoses over time are not an answer to a question, but rather the beginning of a question.
The rising rates of anxiety and depression ignore sociological factors like increased poverty, longer working hours, rising levels of stress. They ignore how more and more schools are incorporating mental health screening and education, at least at the post-secondary levels.
Let’s look at another statistical trend: the rising rates of childhood asthma. Why is this the case? One might notice that the rates have risen at the same time that the rates of air pollution have risen. Alone this information doesn’t mean much. Have the diagnostic procedures changed at the same time? Further testing must be done in order to ascertain whether there is any actual link between the two ideas.
Keep this in mind the next time someone uses diagnostic increases as reasoning for why ADHD, anxiety, depression, fibromyalgia, and other conditions don’t exist, are over-diagnosed, or as proof of some hypothesis or another. By themselves increased rates of diagnoses indicated nothing other than, there have been more diagnoses. It tells us nothing about why, or what it means. It tells us nothing about whether the disease is actually more prevalent or simple better recognized. Whether the diagnoses are valid or the result of too broad diagnostic criteria. It is just one part of the puzzle, and it is irresponsible to suggest that it in anyway indicates the whole picture.