"magnitude of decrease" is correct and usable in written English.
It is typically used to refer to the size or extent of a decrease. For example, "The magnitude of decrease in sales was surprising."
The magnitude of decrease in HR from control values was similar in both groups.
As the variation increases, the accuracy of all methods decreases and the magnitude of decrease is method dependent.
The magnitude of decrease in stroke volume index with sternal closure correlated positively with end-diastolic area immediately before the closure.
At mid-slope positions the order and magnitude of decrease were organic matter and nutrient cycling, flora and fauna habitat, and moisture retention (26, 22, and 16%, respectively).
The magnitude of decrease in χ due to expansion is observed to increase with increasing compositional gradients in the flow field.
However, for almost all samples (Figure 2) SIRM decreases gradually with no obvious difference in the magnitude of decrease for different groups.
Administering GSI progressively reduced dry matter intake (66%) and, by design, the pattern and magnitude of decreased nutrient intake was similar in PF controls.
The second is that the magnitude of decreased D O2 must be similar in both IH and HH.
The magnitude of decreasing LF and HF was the greatest at 2-hr moving averages for the elderly panel.
After collapsing exposure into tertiles, we found that the magnitude of decreased length of gestation was most pronounced comparing the highest tertile of PCB exposure to the lowest tertile of exposure in linear regression models.
This is in keeping with the magnitude of decreases in arterial oxygenation observed in patients with ARDS due to inhibition of HPV by diltiazem [ 19] or prostaglandin E1 [ 20].
