The unreliability of the bubble devices caused by spontaneous bubble annihilation in a large capacity chip is different from that measured in a small test loop because of the direct interaction between neighboring bubbles. This direct interaction can be separated from the indirect interaction by measuring the individual bit decay rates for different word patterns. Measurement on a 16 micron 20 K bit chip shows that the bubble annihilation rate caused by direct interaction can be several orders higher than that caused by indirect bubble interaction through the remanence effect in the permalloy overlay. Because of this strong pattern dependence, the inverse of the initial slope of the error accumulation (mean step to failure, MSTF) should be used as the comparison parameter to evaluate the long term reliability effects in large capacity bubble memory devices.