Contents
- Index
Ordered Data
Ordered data is when data is collected over time. It may be that 3 samples are collected at 10 points in time. The groups of 3 samples are referred to as subgroups. It may be that the underlying data fits the normal distribution, but if a shift occurs in the middle of collecting the data, the resulting histogram can appear to have multiple peaks (modes). Such data is called bi-modal or multi-modal. As a result, it is likely to fail a normality test.
Such multi-modal data may pass the Skewness-Kurtosis Specific test and you may be able to proceed with a variables sampling plan or normal tolerance interval. To determine if a shift occurred, the subgroup each value is from should be entered in the Order column of the Data window. Then an analysis for shifts over time is automatically performed and displayed in Tab 4 of the Test Distribution window.
The difference between groups and ordered data is that groups are categories that are unordered whereas ordered data consists of subgroups that are ordered relative to time. Both can produce multi-modal data.