![]() ![]() Understanding: Defect, Unit and OpportunityĮvery process should have definitions for defect, unit and opportunityįirst: understand the needs of process' customers (listen to the voice of the customer….). 1,75 minutes is the Upper Specification Limit. SuperBank may decide to establish, as a target, that Customer Waiting Time at SuperBank Tellers should not exceed 1,75 minutes.Īny Waiting Time longer than 1,75 minutes would fall out of specifications. There may be a Lower Specification Limit and an Upper Specification Limit. Limits may be associated to Specifications. Specification: a criterion that is to be met by a part, or a product, or any feature of a process.This means that the "Carrying-out-a-Teller-transaction" process at BankExtra is more " stable" than at SuperBank (for a number of contributing factors). ![]() A wider Sample of Customers' Waiting TimeĪnd the results of the exercise would be the same as in the example, the net conclusion is that ExtraBank Customers stand a high chance (more than double) to wait less for a Teller transaction than SuperBank Customers - in spite of the "average" Waiting Time being the same in the 2 cases (the 2 Banks have the same measures of central tendency). If the exercise would be extended to consider: The Standard Deviation is lower: 0,22 minutes (or 40% of that of Superbank) The range is lower: 0,75 minutes (compared to 2,25 minutes of S.Bank) The mode is the same: 2,15 minutes (4 times) SuperBank want to compare their Teller Process Performance with that of their competitor, BankExtra Ltd.Īn observer records ("incognito") the following values of Customer Waiting Time in the same Day as from the same Time (9:30 am):ġ,85 1,85 1,95 1,95 2,00 2,05 2,10 2,15 2,15 2,15Ģ,15 2,20 2,25 2,30 2,35 2,40 2,45 2,55 2,55 2,60 Standard Deviation from the mean = 0,57 minutesĮxample of practical use of Standard Deviation. The standard deviation of a set of N sample's values is a measure of variation of values about the mean, and is defined by the following formula: Standard Deviation σ: a significant measure of variability.NB: to understand process' variation, mean and mode are often meaningless, and the range may be misleading Range: is a measure of "dispersion" which is the difference between the largest observed value and the smallest observed value in a given Sample.Mode: the most frequent Value of a variable in a DistributionĬustomer Waiting Time in minutes at SuperBank Ltd.on that Day, at that Time, and for that Sample of Customers was ![]() The "mean" Customer Waiting Time at SuperBank Ltd. For a number N of variables x i the Mean is
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