This has become much less frequent since the 1940s.

And in the last few weeks I'd noticed that incidents like this had become more frequent.

Why do you believe the incidents have become more frequent?

But these cases seem to have become less frequent in recent years.

Innocent lives are lost in religious and communal violence, which has now become all too frequent.

Major natural disasters became more frequent and helped change public opinion.

As the months passed, my walks to the window at the far end of the hallway became more frequent.

By a year or so later, apparently, such incidents had become frequent.

However, in recent years, the 23 March issues have become less frequent.

Another treatment, which has become more frequent in recent years, is lead glass filling.