Beware of Confounding Variables If I wanted to prove that smoking causes heart issues, what are some confounding variables? The object of an experiment is to prove that A causes B. A confounding variable is anything that could cause change in B, that is not A. Lifestyle and family history may also effect the heart.
Random Assignment Once you have a random sample, randomly assigning them into two groups helps control for confounding variables. Experimental Group v. Control Group. Group Matching
Confounding Variables: Environmental Differences Any differences in the experiment s conditions--between the experimental and control groups Differences include temperature, lighting, noise levels, distractions, etc. Ideally, there should be a minimum of environmental differences between the two groups.
Hawthorne Effect But even the control group may experience changes. Just the fact that you know you are in an experiment can cause change. Individuals may change their behavior due to the attention they are receiving from researchers rather than because of any manipulation of independent variables. Whether the lights were brighter or dimmer, production went up in the Hawthorne electric plant.
Participant Bias Tendency of subjects to respond in certain ways because they know they are being observed The subjects might try to behave in ways they believe the researcher wants them to behave Can be reduced by naturalistic observation or BLIND PRODCEDURE» Blind procedure: participants are ignorant (blind) to the expected outcome.
Experimenter Bias Another confounding variable. Not a conscious act. Double-Blind Procedure. (Participants and data collectors blind to expected outcome)
Other Confounding Variables Placebo effect You think you are receiving the real drug and actually show signs of the experimental group.
Placebo Effect Play The Placebo Effect: Mind-Body Relationship (9:14) Segment #3 from The Mind: Psychology Teaching Modules (2 nd edition) http://www.learner.org/resources/series1 50.html?pop=yes&pid=1610# F11 Ctrl +
Replication Repeating the experiment to determine if similar results are found If so, the research is considered reliable.
Correlational Method Correlation expresses a relationship between two variable. Does not show causation. As more ice cream is eaten, more people are murdered. Does ice cream cause murder, or murder cause people to eat ice cream?
Types of Correlation Positive Correlation Negative Correlation The variables go in The variables go in the SAME direction. opposite directions. Studying and grades hopefully has a positive correlation. Heroin use and grades probably has a negative correlation.
Data Data showing height and temperament in people. 13
Scatterplot The Scatterplot below shows the relationship between height and temperament in people. There is a moderate positive correlation of +0.63. 14
Correlation When one trait or behavior accompanies another, we say the two correlate. Indicates strength of relationship (0.00 to 1.00) Correlation coefficient r = + 0.37 Correlation Coefficient is a statistical measure of the relationship between two variables. Indicates direction of relationship (positive or negative) 15
Scatterplots Perfect positive correlation (+1.00) Scatterplotis a graph comprised of points that are generated by values of two variables. The slope of the points depicts the direction, while the amount of scatter depicts the strength of the relationship. 16
Scatterplots Perfect negative correlation (-1.00) No relationship (0.00) The Scatterplot on the left shows a negative correlation, while the one on the right shows no relationship between the two variables. 17
Correlation and Causation or 18
Correlation Coefficient A number that measures the strength of a relationship. Range is from -1 to +1 The relationship gets weaker the closer you get to zero. What would a zero correlation mean? Which is a stronger correlation? -.13 or +.38 -.72 or +.59 -.91 or +.04