Page 126 - Foundations of Cognitive Psychology : Core Readings

Experimental Design in Psychological Research 129

Use a line graph if your variables are continuous. The lines connecting your
plot points imply a continuous variable. Use a bar graph if the variables are
categorical,so that you don’t fool the reader into thinking that your observa-
tions were continuous. Use a bivariate scatter plot when you have two contin-
uous variables,and you want to see how a change in one variable affects the
other variable (such as how IQ and income might correlate). Do not use a
bivariate scatterplot for categorical data. (For more information on good graph
design,see Chambers et al. 1983; Cleveland 1994; Kosslyn 1994).
Once you have made all your graphs,look them over for interesting patterns
and effects. Try to get a feel for what you have found,and understand how the
data relate to your hypotheses and your experimental design. A well-formed
graph can make a finding easy to understand and evaluate far better than a dry
recitation of numbers and statistical tests can do.

Acknowledgments
This chapter benefited greatly from comments by Perry Cook,Lynn Gerow,Lewis R. Goldberg,
John M. Kelley,and John Pierce. During the preparation of this chapter,I received direct support
from an ONR graduate research fellowship (N-00014-89-J-3186),and indirect support from CCRMA
and from an ONR Grant to M. I. Posner (N-00014-89-3013).

References
American Psychological Association. (1992). ‘‘Ethical Principles of Psychologists and Code of Con-
duct.’’ American Psychologist, 47,1597–1611.
American Psychological Association. (1994). Publication Manual of the American Psychological Asso-
ciation. Fourth edition. Washington,D.C.: American Psychological Association.
Butler,D.,and W. D. Ward. (1988). ‘‘Effacing the Memory of Musical Pitch.’’ Music Perception, 5(3),
251–260.
Chambers,J. M.,W. S. Cleveland,B. Kleiner, and P. A. Tukey. (1983). Graphical Methods for Data
Analysis. New York: Chapman & Hall.
Cleveland,W. S. (1994). The Elements of Graphing Data. Revised edition. Summit,N.J.: Hobart Press.
Cohen,J. (1994). ‘‘The Earth Is Round (p <:05).’’ American Psychologist, 49,997–1003.
Cozby,P. C. (1989). Methods in Behavioral Research. Fourth edition. Mountain View,Calif.: Mayfield
Publishing Co.
Daniel,W. W. (1990). Applied Nonparametric Statistics. Second edition. Boston: PWS-Kent.
Deutsch,D. (1991). ‘‘The Tritone Paradox: An Influence of Language on Music Perception.’’ Music
Perception, 84,335–347.
Deutsch,D. (1992). ‘‘The Tritone Paradox: Implications for the Representation and Communication
of Pitch Structure.’’ In M. R. Jones and S. Holleran,eds., Cognitive Bases of Musical Communi-
cation. Washington,D.C.: American Psychological Association.
Fisher,N. I. (1993). Statistical Analysis of Circular Data. Cambridge: Cambridge University Press.
Fletcher, H.,and W. A. Munson. (1933). ‘‘Loudness,Its Definition, Measurement and Calculation.’’
Journal of the Acoustical Society of America, 72,82–108.
Glenberg,A. (1988). Learning from Data: An Introduction to Statistical Reasoning. San Diego: Harcourt,
Brace,Jovanovich.
Hayes,W. (1988). Statistics. Fourth edition. New York: Holt,Rinehart and Winston.
Hempel,C. G. (1966). Philosophy of Natural Science. Englewood Cliffs,N.J.: Prentice-Hall.
Hunter,J. E.,and F. L. Schmidt. (1990). Methods of Meta-analysis: Correcting Error and Bias in Research
Findings. Newbury Park,Calif.: Sage.
Kirk,R. E. (1982). Experimental Design: Procedures for the Behavioral Sciences. Second edition. Pacific
Grove,Calif.: Brooks/Cole.
Kosslyn,S. M. (1994). Elements of Graph Design. New York: Freeman.
Levitin,D. J. (1994a). ‘‘Absolute Memory for Musical Pitch: Evidence from the Production of
Learned Melodies.’’ Perception & Psychophysics, 56 (4),414–423.