Before the study began, all patients received regular replacement therapy with immunoglobulin. Patients were then assigned to one of two groups. One group received 9 months of therapy with standard-dose immunoglobulin, followed by 3 months of the same dose they had received before the study, then 9 months of treatment with a double dose of immunoglobulin. In the second group, the order of low-dose and high-dose therapy was reversed. To ensure that patients, doctors, and nurses were unaware which dose was being administered, the pharmacy made the injections look identical. Researchers recorded the number, type, and duration of infections that occurred, as well as the use of antibiotics, for each patient throughout the study. The lowest level of immunoglobulin in the blood (“trough level”) was evaluated by measuring immunoglobulin levels immediately before each dose of immunoglobulin was given.