Final answer:
The statement is false; controls in an experiment are kept constant to serve as a standard for comparison, not altered. They ensure that the experimental group's differences can be attributed to the tested variable.
Step-by-step explanation:
The statement 'Controls are altered until residual risk is at an acceptable level' is False when it comes to scientific experimental design. In an experiment, controls are not altered; they are kept constant to ensure that any changes in the experimental group can be attributed to the variable being tested. The purpose of a control group is to be a standard for comparison and it must remain unaltered throughout the experiment. The control group must be identical to the test group except for the one variable being experimented upon. This setup allows for a clear understanding of the direct effects of the independent variable on the dependent variable.
It is also important to note that experimental controls do not eliminate the need for statistical tests or large sample sizes; they serve to reduce variability by ensuring that the groups under study differ only in the one variable of interest. This allows for more accurate interpretation of the results.