1. The Experimental Method
Psychology: Chapter 2, Section 4

2. The Experimental Method
As mentioned before, correlation does not always indicate causation
The method that researchers use to answer questions about cause and effect is the experiment
In an experiment, participants receive what is called a treatment, such as a change in room temperature or a new drug
Researchers carefully observe participants to see what changes may have occurred (if any)

3. Limitations of the Experimental Method
There are several limitations of the experimental method
The conditions created in an experiment may not reflect conditions in real life
Experiments must simplify conditions to yield information about cause and effect
Nevertheless, despite these limitations, experiments do yield useful and helpful information

4. This person doesn’t normally walk around with wires on his head, and experiments may not always be able to replicate real life situations very well, but they do offer advantages with finding cause and effect

5. Independent and Dependent Variables
Experiments contain variables, which are factors that can vary, or change
The independent variable is the factor that researchers manipulate to observe its effect
If researchers want to see the effect of amount of sleep on people's ability to drive through a maze, the independent variable is the amount of sleep, which researchers manipulate to see the effect
The dependent variable depends on the independent variable
In this case, the people’s ability to drive through the maze is the dependent variable, as it depends on the amount of sleep people get

6. Independent and dependent variables can be recorded on a table, and displayed on an x-y axis

7. Experimental and Control Groups
Controlled experiments are the most informative kind of experiments, in that they use experimental and control groups
Members of the experimental group receive the treatment
Members of the control group do not
Researchers try to make sure all other conditions are the same for both groups
This way, researchers can conclude that the experiment’s results are caused by the treatment, not by something else
Participants are randomly assigned to each group, and they do not know which group they are in

8. Control groups allow us to see the effects of a treatment with everything else being equal
What conclusion could we draw regarding the treatment given to bring the levels of creatine phosphokinase into the normal range?

9. Describe what this graphic means:

10. The Placebo Effect
Our expectations affect how we feel or what happens to us
A placebo is a substance or treatment that has no effect other than the person’s belief in it
A person may believe that taking a pill will get rid of a headache, and in taking a sugar pill with no medicine, begin to feel better
Researchers should be aware of this effect when conducting experiments– just the fact of someone coming to an experiment will have an effect on that person

11. Here’s an interesting article about the placebo effect
Here’s an interesting article about the placebo effect. Why do you think placebos work?

12. Single-Blind Studies
To counteract expectations and the placebo effect, researchers may not tell participants what kind of treatment they are receiving
Because participants are unaware (or blind) if they are in a control or in an experimental group, it is called a single-blind study
In a typical single-blind study, half of those given the real drug are told they are being given a placebo, half of those given a placebo are told they are being given the real drug, while the other halves are told what they are really being given

13. In a single blind study, participants are randomly given the test treatment or placebo, and then followed up with either the test treatment or the placebo

14. Double-Blind Studies
Researchers may also have expectations regarding the experiment that may bias the results
In this case, the researcher should also not know who is being given the placebo and who is being given the real treatment
A double-blind study is where both the participants and the experimenters are unaware of who is in the control group or experimental group
The Food and Drug Administration (FDA), which tests the safety of all drugs in the United States, requires that all studies be done as double-blind studies

15. A double-blind study is essentially the same as a single-blind study, except that the results are further secured by the experimenter also not knowing if the test or the placebo is being administered

16. Central Tendency and Dispersion
One of the purposes of research is to be able to generalize and find out what a typical, or average, response is
Researchers ascertain the central tendency (the general area where responses tend to be)
The most common measures of central tendency are mean, median, and mode
The mean is the average, the median is the middle number when the numbers are put from highest to lowest, and the mode is the number that occurs most often
Researchers are also interested how spread out the data is, and use the range and standard deviation to measure this
The range is simply the smallest number subtracted from the largest number
The standard deviation measures how far each item of data is from the mean

17. Mean Median and Mode, along with Range, tell us about the Central Tendency, or what a typical number/ answer is

18. Assessment
Complete #1-3 on page 44