Which part of the scientific method involves actively manipulating variables?

The part of the scientific method that involves actively manipulating variables is the design of the experiment. During this stage, a researcher creates an experiment where specific variables, often referred to as independent variables, are intentionally changed to observe the effects on other variables, known as dependent variables. This manipulation is crucial because it allows scientists to establish cause-and-effect relationships and determine how different conditions affect outcomes.

When designing the experiment, researchers must carefully plan how they will control and manipulate these variables to ensure that the results are valid and reliable. This includes establishing control groups and ensuring that all extraneous variables are accounted for or minimized, enabling a clear interpretation of the effects that the manipulated variables have on the experiment's results.

The other options represent different stages of the scientific process. Gathering data involves collecting measurements without manipulation, drawing conclusions is about analyzing results after the experiment has been conducted, and formulating the theory refers to developing explanations or models based on the gathered evidence. Each of these stages serves a distinct purpose within the scientific method, highlighting how manipulating variables is specifically tied to experimental design.