All reported disease statistics are subject to error, but VD statistics suffer more than others. People with reportable diseases do not always reach a doctor pr a clinic, or may go undiagnosed or mis-diagnosed. There is both under-reporting (cases missed) and over reporting (mistaken diagnoses). The first group is usually larger than the second, and the statistics are therefore usually too low. The error tends to get smaller as the disease gets more severe; mild cases are least likely to be seen by a doctor, while fatal illness is hardly ever missed. Special efforts are made to spot highly communicable diseases, and everybody concerned usually cooperates in the public interest. There are exceptions. When bubonic plague appeared among Chinese immigrants in San Francisco in 1900, strenuous efforts were made by the local authorities to hide the fact it was bad for business; and in the 1970 cholera outbreak in the Middle East and Africa there were charges that cases were unreported, presumably because the epidemic was bad for tourism. But statistical reports give us complete confidence that polio has almost disappeared from the United States, that malaria is coming in from overseas, and that diphtheria is kicking up again in areas where immunization of children has been neglected. Today when sporadic cases of bubonic plague appear, as they have been doing in New Mexico, or when a few people come down with botulism, as happened not long ago in Illinois, they are unlikely to go unrecognized or unreported.

The VD problem has always been and still is more like plague among the San Francisco Chinese in 1900 and cholera in Africa, and for reasons more complex and devious. An aroma still clings to VD which, though a long way from being the same, yet brooks comparison with that which emanated from leprosy in the Middle Ages. As the smog of today's cities chokes up the air passages of sensitive people, so does this stink of VD clog the channels of statistical communication.

For one thing there is an indeterminate number, presumably relatively small, of cases falsely reported as positive, especially for gonorrhea: instances reported without adequate diagnostic tests among sexual partners or assumed partners of known cases, or on the basis of clinical or technical errors. There is probably a good deal of gratuitous assumption of gonorrhea among prostitutes and female prisoners. But the total of such false positives is offset many times over by failure to report confirmed cases of both gonorrhea and syphilis. On top of this we have people with VD who go untreated or are treated by quacks, as well as patients, especially women with gonorrhea, whose illness is simply not detected. Most observers hold that failure to report known cases is the largest source of error in the statistics, and it is this error that the United States authorities have attempted to measure. The non-reporters are, of course, private physicians protecting their patients against disclosure of what is treated by society as a crime.