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I have a dataset of observations taken at random time points across a wide range of time. These are X-rays taken in a fashion that, sadly, is a bit random (clinic can get a bit manic).

I have 70 patients. Each patient has between 2 and 8 images. This means about 300 images. The image capture time is random, but always between 1 and 80 months from the first image.

We have a series of morphological measurements we have extracted from each image. SC_1 is the first metric, we have about 18 to look at.

I want to determine if the measurements we are obtaining are changing significantly over time. I expect that around half of them will show a substantial change in morphology after 6 months. But I need to see if this is true, and then identify those patients who did change significantly.

[Data structure][1]

I have tried plotting the data - it is a bit of a mess unfortunately because there are more patients than colours to choose, and the varying time-frame. But some are definitely are showing change over time, while others are not.

Plot of all images colour coded for the patient

I am at a loss to figure out the best way to quantify the change for each patient. I was thinking perhaps take the percentage change for each patient, between the first and last image - and assigning this number to each patient? Or take the standard deviation for each patient's measurements over time?

Or is there a more sophisticated method? If I can get a pointer in the right direction, I'd happily learn a new method (e.g. some form of time series). It is just getting to the point of knowing which methods to look at.... I will have about double to dataset in a few months though....

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One of the possible methods you might consider here is a multi-level linear models (I've added these tags to your question). In brief, your model will have a response variable of the morphological measurement (say SC_1), and there will be predictor variables for the individual and the time of the x-ray measurement. The multi-level model will allow you to run this model in such a way that it will estimate a random intercept and/or slope for each patient. This is somewhat more sophisticated than running just a regular OLS regression, but this should get you pointed in the correct direction.

Happy to share more or update this answer as needed.

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  • $\begingroup$ Thank you Gregg, I am just doing the required research. I will post my results and solutions later - should someone else find this thread and seek similar solutions. Many thanks! $\endgroup$
    – Maks Hall
    May 26, 2023 at 12:42

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