What is the term for a research method where one or more factors are manipulated to observe effects on a dependent variable?

The correct answer is the term "experiment." In research, an experiment is a systematic method that involves manipulating one or more independent variables to observe the effect of these manipulations on a dependent variable. This method allows researchers to establish cause-and-effect relationships by controlling for other variables that might influence the outcome.

Experiments typically involve the creation of conditions under which variations can be introduced and measured, often in a controlled environment. For example, by changing the amount of sunlight a plant receives (independent variable) and measuring its growth (dependent variable), researchers can draw conclusions about the relationship between sunlight and plant growth.

Other methods, such as surveys, case studies, and cross-sectional studies, do not involve manipulation of variables in the same way. Surveys are primarily descriptive and gather data through questionnaires without altering conditions. Case studies focus on an in-depth analysis of a single case, and cross-sectional studies provide a snapshot of a population at a single point in time, lacking the experimental control needed to determine causality.