The phrase "differ in the extent" is correct and usable in written English.
You can use it when discussing variations or differences in degree or scope between two or more subjects.
Example: "The two studies differ in the extent of their sample sizes, which may affect the results."
Alternatives: "vary in degree" or "differ in scope."
We selected two different sites for biting that differ in the extent of vascularization: the ear and the back.
Expression of the ANT genes was compared across two apple genotypes, 'Gala' and 'Golden Delicious Smoothee' (GS), which differ in the extent of fruit growth, largely due to differences in cell production.
We also examined sex differences in other-objectification; or put another way do men and women differ in the extent to which they objectify Halloween-costumed women (judge the costumed women in terms of their sexual appeal)?
Physicians tend to have fairly differing views on the time a client needs for recovery and also differ in the extent to which they take account of personal circumstances.
Such differences in the LIE capability made available to EPs could explain why physicians differ in the extent to which they use these systems in their daily practice.
Indeed, parasitic plants differ in the extent to which they depend on their hosts for nutrients.
Systems of constitutional judicial review also differ in the extent to which they allow courts to exercise it.
Yet it is well known that mammals differ in the extent to which their behaviour is affected by odours.
Communities differ in the extent to which they stress the importance of individual experience of the divine, as distinct from adherence to a creed expressing the basic beliefs of the community.
The technologies do, however, differ in the extent to which they can provide these services.
They differ in the extent to which a profit orientation is prominent.
