Measured occlusion effects in all 37 ears. Thin lines represent individual ears, thick lines 5- 50- and 95-percentiles of all level differences at frequencies where data from at least 10 ears were considered valid according to Section 2.6.3. Top: sequentially measured OEs (Eqs. (6), (9)), middle: simultaneously measured OEs using the device microphone as reference (Eq. (7) and first equation in Eq. (10)), bottom: simultaneously measured OEs using the probe tube microphone in the open contralateral ear as reference (Eq. (8) and second equation in Eq. (10)).