Sometimes disorders show diagnostic inflation and sometimes deflation, and neither is more common than the other. Overall, diagnosis have not consistently inflated from DSM-III to DSM-V. 

More on data 

Of 123 comparisons of the diagnostic rates of a disorder from one condition to the next, 26.8% were significantly different, and 76.4% had a 10% change in diagnostic rate. Thus, DSM revisions have had substantial effects on rates of diagnosis. 

University of Illinois at Urbana-Champaign

A systematic increase in rates of diagnosis based on changes in diagnostic criteria alone.

Diagnostic inflation

Fabiano, F., & Haslam, N. (2020). Diagnostic inflation in the DSM: A meta-analysis of changes in the stringency of psychiatric diagnosis from DSM-III to DSM-5. Clinical Psychology Review, 80, 101889. https://doi.org/10.1016/j.cpr.2020.101889

Diagnostic inflation in the DSM: A meta-analysis of changes in the stringency of psychiatric diagnosis from DSM-III to DSM-5

A common complaint is that the new DSM editions have invalidly increased the prevalence of mental disorder, either by adding new conditions or by loosening the diagnostic criteria for existing conditions. 

Diagnostic inflation in DSM-5

Chair of the DSM-IV Task Force.

He expressed concerns about diagnostic inflation. He and some others instituted a campaign to "save normality" from DSM's expansionism and interpreted the rising prevalence of mental disorders as evidence that normality is endangered. 

Allen Frances

Data on diagnostic inflation

Many physical illnesses can cause symptoms that are similar to the symptoms of psychological disorders, and there is a risk of misdiagnosing them as such. Around 12% of psychiatric admissions are caused by unidentified physical illness, resulting in the worsening of the symptoms. Therefore, the psychiatrist needs to be aware of such illnesses and their symptoms to be able to order physical tests and rule out any possible physical illnesses before diagnosing the patient.

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