Chapter 1 - Introduction to Statistics - 1-4 Collecting Sample Data - Basic Skills and Concepts - Page 32: 2

An experiment which has an imposed treatment reduces the possibility of lurking variables. Conducting an observational study would not ensure that fruit consumption is associated with weight loss, but conducting an experiment which reduces the effects of other variables that may be associated with weight loss could show a correlation between fruit consumption and weight.

An experiment which has as imposed treatment, reduces the possibility of lurking variables. Conducting an observational study would not ensure that fruit consumption is associated with weight loss, but conducting an experiment which reduces the effects of other variables that may be associated with weight loss can show a correlation between fruit consumption and weight.