Use the range rule of thumb to determine whether 4 is a significantly high number of sleepwalkers in a group of 5 adults.
Refer to the accompanying table, which describes the numbers of adults in groups of five who reported sleepwalking (based on data from "Prevalence and Comorbidity of Nocturnal Wandering In the U.S. Adult General Population," by Ohayon et al., Neurology, Vol. 78, No. 20).
x P(x)
0........................0.172
1........................0.363
2........................0.306
3........................0.129
4........................0.027
5........................0.002