Bland-Altman difference Plot problem with code

[Eli Omo]

Hi all,

I have been trying to draw a bland -altman difference plot

Code:

 batplot systolicdifference gestationweek, title(Difference in systolic blood pressure per week ) notrend xlab(16(2)43) moptions(mlabp(9))

To clarify further the variable

systolic

already includes the difference ( y-axis) and the

gesationweek

is on the x-axis as I am looking for the difference per gestation week but some reason the code is not working.

Any assistance will be greatly appreciated.

[Leonardo Guizzetti]

What you describe is not a Bland-Altman plot, also called a mean-difference plot (ascribed to Turkey). In this plot, two measures of the same quantity (e.g., by two raters) have their difference plotted against their average. This is easy enough to plot using -twoway scatter-.

What you describe is altogether different, where you seem to want to examine the time trend of differences. This again can be plotted with the same graphing command, but you should also consider some appropriate regression model if you want to quantify this trend.

Lastly, -batplot- is not a command that is part of official Stata, so if it is user-contributed then your are asked to describe from where you found it.

[Eli Omo]

Thank you very much I think I want to examine the time trend of differences so I'll apply your advice