Defining Variables for C (Attribute) Chart - Quick Tab

Select the Quick tab of the Defining Variables for C (Attribute) Chart dialog box to access the options described here.

Input data are counts or raw data (with piece info)

The settings of these option buttons determine whether Counts or Raw data are being used for the computations. Note that with the Counts option button selected, Statistica assumes that each observation in the input data represents one sample, and the counts specified for the sample will be used to construct the respective chart; the specification and interpretation of data when the Raw data format is specified does not make this assumption and is more flexible (see next paragraph).

Raw data reading for attribute charts (database format)

When the Raw data format is specified, Statistica will count the number of pieces (computer chips identified in a piece identifier variable) with defects greater than 0 (computer chips with one or more defects as specified in a defect indicator variable); samples of pieces ( batches of computer chips) are identified in a sample identifier variable. Note that in this method of data reading, the unit of analysis is the individual piece and not the number of defects: each piece is counted as being defective only once if the defect indicator variable shows a value greater than 0 (and regardless of the actual value greater than 0). For example, a computer chip (identified with a unique piece ID) that has 100 defects is counted as a single defective observation, in the same way as a computer chip would be counted with a single defect. Hence, this method of reading and tabulating data is very flexible, and particularly well suited for processing automated data streams.

Variables

 Click the Variables button to display a standard variable selection dialog box. If you have the Counts option button selected, you can select Variable with counts and Part identifiers (optional for short run charts). If you have the Raw data option button selected, you can select Defect indicator, Piece ID's, Sample ID's, and Part identifiers (optional for short run charts).

Counting of pieces in raw data reading

When reading the data in raw data format (as selected via the respective Input data option), Statistica will compare piece id's of consecutive observations to determine whether a defective piece is new or old. Note that in raw data reading, the chart is constructed for the number of defective pieces, regardless of how many defects were found for each piece (as specified in the defect indicator variable). These piece ID's do not have to be unique; instead, every time that the piece id's for consecutive observations differ, the program assumes that the observation represents a new piece. If you are in doubt about how exactly data are interpreted in this mode of reading, you should try a simple artificial data set to confirm how data are interpreted and defects are counted.

Constant number of samples per part

 If this check box is selected and no part identifier variable is selected, you can specify here a fixed number of consecutive samples for each part. For example, if your input data consist of batches with different specifications (i.e., different parts) from which a fixed number of samples is automatically drawn, then you can select this option so that on reading the data each chunk of k consecutive samples is automatically assigned to the same part.