She had observed the need over years of working in the field herself.

This is 50% larger than the average rate observed over the 20th century.

The same trend has been observed in China over a similar period.

We've been observing them all over the sky since the 1960s.

I had observed him over the course of five days and his behavior never varied.

In this condition it can be observed over a much longer period.

Also around 230 species of birds have been observed here over the years.

More than a thousand such events have been observed over the past ten years.

But this is not in line with the statistics observed over more than a century.

This is indeed the average rate as observed over the past 27 centuries.