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measurements

Ted

For group of cancer patients measured the number of metastases before and after treatment.

The character of changes (less metastases or more metastases after treatment) is an assessment of the effectiveness of the treatment.

What kind of stat. analysis conduct?

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txnelson

Using your wide format, check out

Analyze==>Specialized Modeling==>Matched Pairs

Ted

Thanks Jim! I will try

cwillden

Matched Pairs is the first thing I would think of, but I you need to check the appropriate assumptions. If you plot the difference (before-after) against the before count, you get this: Before vs Difference.PNG

The good news is, whatever this treatment is, sure seems to reduce the number of metstases. However, the fact that the effect of the treatment is also a function of how bad the patient's case is beforehand, you need to account for that in the test/model.

In the wide-format data, add a column that computes the difference. This is your response. Then, fit a regression line to the differences by the before count. You'll find that the slope term is 0.357, which means for every additional pre-existing metastasis, the treatment will reduce 0.357 more mestastases on average. See the attached script.

My only concern with this approach is the independence plot. Are these patients listed in any kind of time order? If so, there might be an issue there, especially since the last 2 patients are the ones with increased metastases.

Ted_WIDE-FORMAT.jmp

Ted

Cameron, my deep gratitude for your approach.
"Are these patients listed in any kind of time order?" No!

dale_lehman

Isn't there a time variable missing from this data? I'm not sure how meaningful it is to measure the number of metastases without recording when he measurements are taken. Were they all taken at the same time after treatment? Given that two patients died, it seems to me that there is at least some time variation in the data (as well as some censoring). So, while the matched pairs approach may give you a crude estimate of whether or not the treatment reduces metastases, I'm not sure the precise measurements are meaningful without knowing more about the timing of the measurements.

Ted

I understand well the notes about additional elements of the model (in particular, time). Thank you!