Last summer's American drought, they say, was most likely a result of natural variation.

Defining the natural variation of lake levels was considered very important.

The project did not operate for a long enough time to show statistically any change from natural variations.

What if the natural variation in a disease's course is behind the placebo effect, they asked?

It is accepted that within any given population there are natural variations in health status.

There is a wide natural variation in results from healthy test subjects.

This range might be either natural or controlled variations in environment.

The differences are due not only to natural developmental variation.

Several data are required to overcome natural variation within a population.