The phrase 'increase proportionately' is correct and can be used in written English.
It is used to indicate that something has grown in a similar ratio as something else. For example, "As demand for the product increased, prices went up proportionately."
The reason is simple: if workers produce more and more per hour (increased productivity), but their incomes don't increase proportionately, then there are no consumers to buy the increasing volume of goods and services they produce.
As our electronic tethers grow ever tighter, the energy disruptions increase proportionately.
As the care workforce grows in coming years these costs will increase proportionately.
But as the motor's size grows, magnetic losses increase proportionately, reducing efficiency.
In a reverse split, the total of a corporation's outstanding shares is reduced in the expectation that the share price will increase proportionately.
Those who identified themselves as being of Sub-Saharan African ancestry in the 2000 census numbered more than 122,400 citywide, up 127percentt from 1990 and the largest increase, proportionately, of any ancestry category, according to city demographers.
Human impacts on the planet have increased proportionately.
His political expenditures and his expectations have increased proportionately.
As temperatures rose, the control subjects' perspiration rates increased proportionately; their core temperatures stayed constant.
"The percentage of people who take it increases proportionately with age," said Laura Ellington, the school's founding director.
Reeves himself became the muscle-man most in demand, but as his salary increased proportionately, producers were signing up anybody who had won a bodybuilding contest.
