Say you are testing a new kind of painkiller. you have 60 volunteers, 30 get the new medicine, and 30 a placebo. double blind means that the volunteers do not know what kind of pill they are receiving, nor do the people recording the patients' reports of pain relief. This is so that the people recording the results do not influence the volunteers responses or take biased notes. also, the volunteers don't imagine that they have less pain just because they know they have the new medicine. BUT, for each volunteer finished, the data collected, those data will keep in the dark until the whole study finished? Or the data analyzer can know each patient data, when he/she finished.
Wild, you are close but not quite exact. If one is testing a new pain killer, not only do the patients not know what they are receiving (drug or placebo), but the doctors providing the treatment do not know what they are administering. This by definition must automatically filter to those recording the data.
Thanks zing, but if each patient data can not reveal even the patient completed 6 weeks study, why one center in Texas knew that one patient received Z160 had only pain score of 2 on 10 pain scale, and another patient received placebo quit study?
Collecting data on patients who completed 6 weeks study will not interfere the double blind study when assign to patients and doctors, data collectors do not communicate will them.