APD can affect both children and adults, although the actual prevalence is currently unknown.

Consequently, variability exists within the scientific literature as to the actual prevalence of referred itch in humans.

The actual prevalence of this practice is difficult to ascertain.

The actual prevalence of Klippel-Feil syndrome is unknown due to the fact that there was no study done to determine the true prevalence.

However, the actual prevalence varies between regions.

The actual prevalence of HIV may be higher in these groups as data collection remains difficult and is limited by sampling methods.

In 2004, it was created in the laboratory, but it is still not clear what its actual prevalence in nature is.

The actual prevalence of food allergies is estimated to be approximately 6% in infants and children and 3.7 % in adults.

The performance of a partial recording system is affected by the actual prevalence of periodontal disease in the population in question.

To that end, efforts are continually made to improve research techniques in order to better estimate the actual prevalence of mental illness.