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Two plots are used to analyze this data, a plot of identity and a BlandAltman plot. The data follows: SUBJECT LARGE MINI 1 494.0 512.0 2 395.0 430.0 3 516.0 520.0 4 434.0 428.0 5 476.0 500.0 6 557.0 600.0 7 413.0 364.0 8 442.0 380.0 9 650.0 658.0 10 433.0 445.0 11 417.0 432.0 12 656.0 626.0 13 267.0 260.0 14 478.0 477.0 15 178.0 259.0 16 423.0 350.0 17 427.0 451.0 The first is called a plot of identity. It is similar to a regression plot, except the line in the plot is a line based on X = Y. If the scatter of points in this plot lies near the line, it indicates that the two ways of measuring PEFR are similar. To display this plot: Step 1: Open BAEXAMP.DBF. Select Analyze/Advanced Regression and Comparisons/Bland Altman/Line of Equality Plot. Step 2: Select the two variables LARGE and MINI. The following plot is displayed: From this plot of identity, you can see that the scatter of points falls close to the line. A second method of looking at this data is with a BlandAltman Plot. This plots the average of the two values by subject against the difference. 95% confidence limits are also calculated and displayed on the graph (Mean difference ± 2 * Standard Deviation) To display this plot (after opening the BAEXAMP DATA): Step 1: Select Analyze/Advanced Regression and Comparisons/Bland Altman/BlandAltman Plot. Step 2: Select the two variables LARGE and MINI. The following plot is displayed:
If the two measures are measuring the same thing in a unbiased way, this plot should show a random scatter of points between the upper and lower confidence limits. The plot above is indicative of a good fit. If there is a pattern to the points, there might be some biased associated with the measurements. This procedure is available in the WINKS Professional edition.

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