Chapter 6

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lesting o Chonge 103Group IGroup 2t questronbecause of1 overcamerg randoml numbersthe test. In:dure using.ting in thee new prodonot dif-.ent by co1-nces in thei: I{J0 5 1 0 1 5 2 0 2 5 0Patienta Current Procedurel New Procedureo Current Procedurel New ProcedureFigure 6.6. Sinultoneous tomporison Test Using Plonned ouping.,n procedurering whetherdlffereni hosoco|sloer oexheme conmenlnboihsts, one wilh3r rnrrryeofscns are heldgroups. Theincluded inIn her test, Dr. Smith purposely set up two groups that had very different conditions.lf the new procedure resulted in improvement in both groups, her degreeof belief would be high that the change would result in improvement in thefuture. To conduct the test, she ran a simultaneous comparison study in bothgroups. Once the patients were selected for a particuiar group, they were randomlyassigned to receive the new or old procedure. The results of the test areshown in Figure 6.6.The run chart shows that the new procedure resulted in improvement in bothgroups. Alrhough the rehabilitation time was generally higher ln group l, thenew procedure stlll resulted in shorter times. Dr. Smith's degree of belief wasincreased that ihe new procedure would result in improvement under the differentconditions to which it would be applied.The possibility exists that the change will show improvement in some plannedgroups but not in others. If this results, the next cycles should be used to studythe relationship between the change being tested and the different conditions inthe groups.Choosing o Studyf experienceThe before-and-after test and the simultaneous comparison can be used in manysituations. Following are some things to consider when deciding which tlpe ofstudy to use:
104 The lnprcvenenl GuideConsider a beJore-and-aJter test uhen:1. The data that are available or that can be collected before the change are sufficienlto lorm the basis of comparison.2. There is a minimal threat of misinterpretation of the results because someexternal event is present on or about the same time the change is made.3. Data will continue to be collected over a long period of time after the changehas been made.4. Large i.mprovements are expected.5. Groups needed for a simultaneous comparison test cannot be isolated-forexample, when a group of mechanics assigned to use an old maintenanceprocedure prefer the new procedure and begin to use it.Consid,er a simultaneous comparison when:I. Two or more alternatives to the current system (for example, two new suppliers)are being tested.2. Only one alternative is being tested but external events pose a threat to theinterpretation of the resuls. A control group (a group using the current system)should be used along with the alternative group being tested.3. There is a desire to include a wide range of conditions in a test during onecycle. This is possible by using planned grouping.Tests in Which More Than hne Chonge is ModeIt is possible to test more than one change at the same time by using a t)?e oftest called a Jactorial expeiment. A factorial experiment provides an altemativeto testing one change at a time. lt allows for the study of the impact of differentcombinations of changes. For example, a factorial experiment could detect thatsome combination of temperature and pressure has the optimal effect on animportant characteristic of a product. A1so, a teacher might want to test havingstudents working in teams versus a standard lecture format and at the same timetest the impact o[ class size. Perhaps, the team approach will result in improvementonly when the class size is small. Although factorial experiments arebeyond the scope of this chapter, many books are available for further study.Evaluotion of the EvidenceThe prediction that a change will result in improvement is based on the knowledgeof the people making the change and the evidence or data that is collecteddurlng the test. In some cases, the evidence is very strong. In the examples inthe last section, the impacs of the chanqes were obvious. The data indicated that
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