<s>[INST] <<SYS>> This is a medical question of type : frequency <</SYS>> How many people are affected by psoriatic arthritis ? [/INST] Psoriatic arthritis affects an estimated 24 in 10,000 people.  Between 5 and 10 percent of people with psoriasis develop psoriatic arthritis, according to most estimates. Some studies suggest a figure as high as 30 percent. Psoriasis itself is a common disorder, affecting approximately 2 to 3 percent of the population worldwide. </s>