'weak effectiveness' is correct and can be used in written English.
You can use it when you want to describe the amount of success a particular action or strategy has had. For example, 'The environmental protection regulations had a weak effectiveness in reducing pollution.'.
The development of gram positive resistance to vancomycin along with possible weaker effectiveness against MSSA have been major reasons not to routinely use prophylaxis [ 32].
Mr Elsby and his co-authors fear that America will be stuck with a "persistent residue of long-term unemployed workers with relatively weak search effectiveness, depressing the strength of the recovery".
Berkeley, the upmarket London housebuilder, was 99th due to weak board effectiveness and low scores on pay and shareholder relations.
The thermal offset between the top and bottom of the crushed rock layer shows that the decreasing trend of soil temperatures indicates a weak cooling effectiveness for the CRBE.
Older generations have weak inhibitory effectiveness and poor stability, but the newer agents are competitive, tight-binding inhibitors with nanomolar Ki values, which interact stoichiomerically with purified recombinant sEH [ 159].
Both of them produced alarmingly weak evidence of effectiveness.
NGO inputs were essential where communities, public health systems and governance were weak and boosted effectiveness in stronger settings.
Studies have shown that the introduction of Medicare Part D has had an impact on the use of drugs with both strong and weak evidence for effectiveness and that there are differences in how sensitive demand is to changes in out-of-pocket cost across drug classes.
This is where parents' educational styles, their effectiveness and weak sides come to light.
