# how to plot BlandAltman, when their sampling sizes are different?.

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Vaishali Ravichandran on 16 Mar 2022
Answered: arushi on 29 Dec 2023
sizes of the data
BFVP_time=1*223
ICP=1*180000
how to match their length and plot blandaltman?

arushi on 29 Dec 2023
Hi Vaishali,
I understand that you want to plot BlandAltman when the sampling sizes are different. Bland-Altman plots are used to compare two different measurements of the same variable to assess agreement. However, for this type of analysis, the two sets of measurements must be paired, meaning that for each measurement in one set, there must be a corresponding measurement in the other set.
When the sampling sizes are different, as in your case where BFVP_time has 223 samples and ICP has 180,000 samples, you cannot directly create a Bland-Altman plot because the measurements are not paired. You need to align the datasets by either:
1. Interpolating or Resampling: If the measurements are taken over time or along a similar continuum, you can interpolate the data from the smaller set to match the larger set's time points or vice versa. This approach assumes that the data points represent some continuous function that can be interpolated.
2. Aggregating: If the larger dataset can be logically divided into groups that correspond to the smaller dataset, you can aggregate the larger dataset. For example, if the ICP measurements are more frequent but correspond to the same time intervals as BFVP_time, you can average the ICP measurements within those intervals to match the BFVP_time data points.
3. Selecting Subsets: If there's no logical way to aggregate or interpolate the data, you might consider selecting a subset of the larger dataset that corresponds to the measurements in the smaller dataset. This approach, however, may introduce bias or lose information.
Hope these suggestions help.
Thank you

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