Under this method, a number of sample lots are drawn one after another from a universe depending on the results of the earlier samples. Such sampling is generally adopted in statistical quality contral. If the first sample is clearly acceptable, no new sample is drawn on the other hand if it is completed unacceptable the lot is rejected. However if the initial oft is of a doubtful marginal character falling in between acceptance and rejection limits, a second on final acceptance or rejection the lot. Such sampling can be based on any of the random or non-random methods of selection.