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Control charts are an important statistical process control tool used to monitor changes in process location and variability. This study addresses issues regarding the proper choice of control chart for efficient monitoring of process variability. The choice of the best estimator to be used for variability charts has not been made clear in literature. We have analyzed the performance of eight control chart structures, based on different estimates of process standard deviation. The performance of control charts is investigated under the existence and violation of ideal assumptions of normality. Control chart constants and factors required for computing probability limits, considering normal and different non‐normal parent distributions, are provided for all variability charts. This study aims at providing guidance to quality practitioners in choosing the appropriate variability control chart for normal and non‐normal processes. Copyright © 2011 John Wiley & Sons, Ltd.

A study was designed to test the egotism hypothesis against the learned helplessness hypothesis while considering developmental variation in reasoning about ability. The egotism hypothesis states that performance impairment after failure follows from attempts to avoid appearing low in ability. The learned helplessness hypothesis states that this performance impairment occurs as a result of the perception of noncontingency. Second and sixth grade children were assigned either solvable or unsolvable Matching Familiar Figures Task items. Performance on a subsequent anagram task constituted the dependent measure. Performance deficits on anagrams following failure on the Matching Familiar Figures Task appeared for sixth graders only. These deficits occurred when the anagrams were purported to be of moderate normative difficulty but not when they were said to be very difficult. Moreover, these performance deficits were apparent only in those sixth graders who had a mature conception of ability. Sex differences in response to the perception of high difficulty were noted. Further consideration led to the conclusion that although the primary findings demonstrate egotism, the sex differences suggest that learned helplessness may also occur under some circumstances.A number of researchers have demonstrated that performance impairment follows from experience with unsolvable problems (for reviews see Abramson, Seligman, & Teasdale, 1978;Wortman & Brehm, 1975). Two hypotheses have been advanced to explain this impairment. In both approaches, effects are dependent on particular cognitions or schemes applied to performance information. These schemes have been shown to vary with age (Nicholls, 1978; Nicholls & Miller, 1984a).

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