What does it mean to say that experimental conditions are controlled? Select True or False for each statement. T/F The test groups consist of the same individuals. T/F The null hypothesis is correct. T/F There is no difference in outcome between the control and experimental treatment. T/F All physical conditions except for one are identical for all groups tested.

Video transcript

Hello everyone. What's our next question? A controlled experiment is simply one in which all factors except the blank are held constant. So a controlled experiment is one where we look at only one thing and how it affects whatever we're studying and then measure the results of changing that one thing. So in the controlled experiment the experimenter controls or changes the independent variable called such. Because we're not looking at how it depends on anything else experimental is looking at that variable and changing it and then seeing what effect that has. The experimenter measures the dependent variable so as a result of changing the independent variable things happen to the dependent variable which is measured while conducting the experiment. Everything else. All the other conditions is held constant so that we're looking at only the result of changes we make to the independent variable. So our example would be you know a seed planted. Um And we see how much growth the plant has based on how much it's watered. So we would say the amount of soil and the amount of sunlight are held constant. The independent variable would be the amount of water that is what the experimental controls different amounts of water given to different plants which have the same amount of soil, the same amount of sunlight and the dependent variable measured by the experimenter would be plant growth which depends on how much water is given. So with that in mind let's look at our answer choices choice A says dependent variable. Well that is not a correct answer that's not held constant. Instead we're measuring how it changes in response to changes made to our independent variable. Choice B is independent variable and that is correct. The independent variable is the one thing not held constant. When we set up the experiment, the independent variable is controlled or changed by the experimenter choice C. Says control variable. The control variable are the variables that are held constant. Like in our example the soil and sunlight choice C. Not correct. Joyce D says categorical variable is categorical variable just refers to a variable that occurs in discrete quantities. So instead of being a continuous like amount of water could be different volumes of water uh including different decimal or fractional values. But a variable like how many plants sprouted. That's categorical. You can't have a fraction of a plant. You'd have either one plant or three plants or zero plants. So that would be an example of a categorical variable but that's not referring to something that is not held constant. It's just a description of a quantity. So Choice D. Is not a correct answer. So again, a controlled experiment is simply one in which all factors except the be independent variable are held constant. See you in the next video