Well, nobody is likely to read this, but I might as well put some of the Markov stuff I learned back in the olden days.
Let us assume:
a) 1000 devices are sold. Of those, Android has 83% market share and Apple has 17% market share.
b) Thus, of the 1000 devices, 830 are Android and 170 are iOS
c) The next year, 91% of Android users stay with Android, but 9% switch to iOS
d) so 91% of 830 = 755 stay with Android, but 9% of 130 = 75 switch to iOS.
e) That same year, only 86% of Apple users stay loyal to iOS.
f) so 86% of the 170 iOS users stick with Apple: 146 people. The other 24 switch to Android.
g) the result is: Android now has 755 + 24 = 779 users, iOS has 75 + 146 = 221 users
The iOS user base increases by 51 people, the Android user base decreases by 51 people.
In percentage terms: iOS is up by 221/170 = 30% increase. Android is down by 9%.
This process can be run iteratively until a balance point is achieved.