The Experimental Method

Psychology: Chapter 2, Section 4

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)

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

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

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

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

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

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?

Describe what this graphic means:

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

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

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

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

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

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

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

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

Assessment

• Complete #1-3 on page 44