There have been a number of studies looking at the lake's environment and water quality.
He published a number of academic studies during this period.
If the number of studies is very large, then more than 3 groups may be used.
A number of other polls and studies have been done in recent years with various results.
Since then there have been a number of other studies.
Overall, however, evidence is still based on a relatively small number of studies.
A number of studies seemed to show that it was effective.
There are a number of studies now which begin to suggest further cause for concern.
A number of studies have been mounted starting in 1981.