"an overall positive effect" is correct and usable in written English.
You can use this phrase when you want to describe the result of a certain action as a positive overall outcome. For example, "The new law had an overall positive effect, allowing more people access to healthcare."
In the end I believe meeting Phil had an overall positive effect on my life.
Transit had an overall positive effect on seed germination.
Combining these intensive and extensive margins gives an overall positive effect of education on the amount remitted.
Their heightened pleasure would doubtless have an overall positive effect on the community.
Thus, unconditionally, liquidity leads to an increase in both exit and voice and so we demonstrate an overall positive effect of liquidity on governance.
Although it depends on the taxa, the production, density and structural diversity of hedgerows each had an overall positive effect.
The main points to emerge from this review of studies on STN-DBS in patients with PD demonstrate an overall positive effect on QoL.
"We are hearing more and more from families we serve that therapy dogs have had an overall positive effect on their children," said Marguerite Colston, vice president of constituent relations at the Autism Society, a national grassroots organization.
While the cash was not used for investment, this does not mean it did not have an overall positive effect on the American economy: shareholders went on to spend this cash.
While we find an overall positive effect of R&D subsidies on SMEs' R&D investment behavior, there is evidence for a crowding out effect for the crisis year 2009.
While clickers had an overall positive effect on student exam performance, we found that this effect was significantly greater in higher-performing students, with lower-performing students showing little-to-no benefit.
