5 Steps to a 5 AP Psychology, 2010-2011 Edition - Laura Lincoln Maitland [33]
Correlation does not imply causation. Correlation indicates only that there is a relationship between variables, not how the relationship came about.
The strength and direction of correlations can be illustrated graphically in scattergrams or scatterplots in which paired X and Y scores for each subject are plotted as single points on a graph. The slope of a line that best fits the pattern of points suggests the degree and direction of the relationship between the two variables. The slope of the line for a perfect positive correlation is r = +1, as in Figure 6.2a. The slope of the line for a perfect negative correlation is r = –1, as in Figure 6.2b. Where dots are scattered all over the plot and no appropriate line can be drawn, r = 0 as in Figure 6.2c, which indicates no relationship between the two sets of data.
Inferential Statistics
Inferential statistics are used to interpret data and draw conclusions. They tell psychologists whether or not they can generalize from the chosen sample to the whole population, if the sample actually represents the population. Inferential statistics use rules to evaluate the probability that a correlation or a difference between groups reflects a real relationship and not just the operation of chance factors on the particular sample that was chosen for study. Statistical significance (p) is a measure of the likelihood that the difference between groups results from a real difference between the two groups rather than from chance alone. Results are likely to be statistically significant when there is a large difference between the means of the two frequency distributions, when their standard deviations (SD) are small, and when the samples are large. Some psychologists consider that results are significantly different only if the results have less than a 1 in 20 probability of being caused by chance (p < .05). Others consider that results are significantly different only if the results have less than a 1 in 100 probability of being caused by chance (p < .01). The lower the p value, the less likely the results were due to chance. Results of research that are statistically significant may be practically important or trivial. Statistical significance does not imply that findings are really important. Meta-analysis provides a way of statistically combining the results of individual research studies to reach an overall conclusion. Scientific conclusions are always tentative and open to change should better data come along. Good psychological research gives us an opportunity to learn the truth.
Figure 6.2 (a) Scattergram for perfect positive correlation (r = +1.0). (b) Scattergram for perfect negative correlation (r = –1.0). (c) Scattergram for no relationship between two sets of data (r = 0).
Ethical Guidelines
Whether involved in research or practice, psychologists need to act responsibly and morally. Studies conducted by Harry Harlow involving rhesus monkeys separated from their mothers and subjected to frightening conditions, studies by Phil Zimbardo involving students role-playing prisoners and guards, and studies conducted by Stanley Milgram in which participants believed they were delivering painful electric shocks to another person were highly publicized in the 1960s and 1970s. Following Milgram’s experiments, members of the American Psychological Association strengthened their ethical guidelines regarding research design, implementation, and practice; and other groups adopted similar guidelines. The guidelines prevent unnecessary deception and pain to humans and other animals, and protect confidentiality.
All public and most private institutions have Institutional Review Boards (IRB) that must approve of all research conducted within their institutions. Boards specifically protect participants by requiring researchers to obtain signed informed consent