What is the difference between a controlled experiment and a natural experiment?
http://en.wikipedia.org/wiki/Natural_experiment
http://www.biology-online.org/dictionary/Controlled_experiment
A controlled experiment and a natural experiment are two different approaches used in scientific research to study cause-and-effect relationships. Here's how they differ:
1. Controlled Experiment:
A controlled experiment is a study where researchers manipulate one or more variables in a controlled setting to observe the effects on other variables. In a controlled experiment, the researcher has control over the independent variable (the one being manipulated) and the dependent variable (the one being measured or observed).
Steps to conduct a controlled experiment:
- Identify the research question and hypothesis.
- Define the independent variable (the one you want to manipulate) and the dependent variable (the one you want to measure).
- Create two or more groups: the experimental group(s) receiving the treatment or manipulation, and the control group(s) not receiving the treatment.
- Randomly assign subjects to each group to minimize bias.
- Apply the treatment or manipulation to the experimental group(s) while keeping the control group(s) unchanged.
- Measure and analyze the effect of the manipulated variable on the dependent variable using statistical techniques.
2. Natural Experiment:
A natural experiment, also referred to as an observational study, occurs when researchers observe events or phenomena that happen naturally, without any deliberate manipulation by the researcher. In a natural experiment, the researcher does not have control over the independent variable, as it occurs naturally in the real world.
Steps to conduct a natural experiment:
- Identify a situation or event in the real world that acts as a natural cause or treatment.
- Observe and collect data on the participants or subjects who are exposed to this natural cause or treatment.
- Identify a control group or comparison group that is not exposed to the cause or treatment.
- Compare the outcomes or effects of the manipulated group (exposed) to the control group (unexposed).
- Analyze the differences and correlations between the groups, looking for relationships or causation.
In summary, a controlled experiment involves manipulating variables under controlled conditions, while a natural experiment involves observing variables that occur naturally without intervention. Both approaches have strengths and limitations, and the choice between them depends on the research question, feasibility, and ethical considerations.