Figure 4

Decreases or increases in Der 1 levels on (a) tape samples from futon or mattress covers and (b) Petri dish samples from 100 cm above the bedroom floor. The “increase” and “decrease” groups respectively include data from patients whose 2010 Der 1 levels rose or fell by more than the 2009 Der 1 levels (intervention group = “With cover”; control = “Without cover”). Numbers in boxes are numbers of patients, and y-axes show percentages of patients. The chi-squared test was used to explore the significance of differences between the two groups. A P value of <0.05 indicates statistical significance.