"significant drop in the number of" is a correct and usable phrase in written English.
It is typically used to describe a significant decrease in the quantity or amount of something. Example: The recent policy changes resulted in a significant drop in the number of students enrolled at the university.
Given the restrictive transfusion policy used in the Netherlands, which has led to a significant drop in the number of blood transfusions [ 11, 20], BSMs are probably used more frequently than strictly necessary on medical grounds.
Australia also brought in mandatory helmet legislation in the 90s and saw a significant drop in the number of cyclists.
Even a significant drop in the number of flights since the economy slowed has not helped much.
AV also led to a significant drop in the number of people voting in Australia – that's why they had to make voting compulsory.
Ucas has reported a significant drop in the number of applications it has received for 2012, compared with the same time last year.
JCQ said this was also partly explained by the significant drop in the number of 15-year-olds taking the exam because of the "first results count" rule.
It is however noteworthy that a significant drop in the numbers of ships and men attached to the thematic fleets is evident between 911 and 949.
Since then, surveys have shown significant drops in the number of New Yorkers who smoke, which antismoking activists attribute largely to the city's actions.
The significant drop-off in the number of new GT structures solved compared to the exponential growth in non-redundant gene sequences is a cause for concern.
The increase in number of scans ordered was accompanied by a significant drop in the diagnosis of PE from 22.6% in 2000 to 13% in 2010.
Rates dropped to 360,000 in 2015, partly because of a significant fall in the number of individuals claiming out-of-work benefits.
