"substantive improvements" is correct and usable in written English.
You can use it when you are talking about improvements that are significant, measurable, and meaningful. Example: Our team has made substantive improvements to the design of the product.
27 While air pollution slowly began to improve during this time period, 22 substantive improvements in air quality did not occur until the start of coordinated government interventions in 2001.
"Cognitive enhancement," they write, "unlike enhancement for sports competitions, could lead to substantive improvements in the world".
He said "an initial analysis of the changes by Hacked Off indicated that there are two substantive improvements in the code and eight weakenings".
Moreover, each country is also assessed in terms of its "stretch", the notion that it went well beyond its starting point and made substantive improvements.
Pentagon officials say that wartime has not derailed their efforts to make substantive improvements in the way that the military tackles domestic violence.
CNN won raves from critics who felt that the stylistic and substantive improvements by Mr. Kellner and Mr. Isaacson complemented its previous strong suit -- global reporting.
In particular we wanted to find out if these improved technologies could lead to a substantive improvement to the level of CSF metabolite coverage achievable by standard metabolomic technologies.
But structured interviews don't always have much in common with the conversations that take place in therapists' offices, and since the publication of the DSM-III, in 1980, no major study has been able to demonstrate a substantive improvement in reliability in those less formal settings.
While numerous studies have shown that C-reactive protein is a marker of cardiac risk, none have shown that it can provide any substantive improvement in identifying people at risk over and above traditional risk factors of diabetes, smoking, cholesterol, blood pressure and obesity.
This is a substantive improvement over our 1999 mass table having rms deviation of 401 keV and mean deviation of 9 keV for 1884 data nuclei.
A fifth participant experienced substantive improvement in diagnostic status prior to the onset of treatment and, though she evidenced continued improvements following treatment, the role of the intervention in such improvements is less clear.
