Correlation and Experimentation Module 6 Correlation and Experimentation

discovering a correlation In a case study: The fewer hours the boy was allowed to sleep, the more episodes of aggression he displayed. In a naturalistic observation: Children in a classroom who were dressed in heavier clothes were more likely to fall asleep than those wearing lighter clothes. discovering a correlation Optional: Click for 3 fictional examples. In a survey: The greater the number of Facebook friends, the less time was spent studying.

Correlation Correlation – a measure of the extent to which two variables change together, and thus of how well either predicts the other. (relationship between two variables) Positive Correlation – relationship between 2 variables in which one variable increases as the other increases (ex) the more one studies the higher the grades Negative Correlation – relationship between 2 variables in which one variable increases as the other decreases (ex) the more one exercises the lower the waist size

Correlation Correlation coefficient – a statistical index of the relationship between two variables Range from -1.0 to +1.0 -1.0 = perfect negative correlation +1.0 = perfect positive correlation Scatterplot – a graphed cluster of dots, each of which represents the values of two variables. The slope of the points suggests the direction of the relationship between the two variables. The amount of scatter suggests the strength of the correlation (little scatter indicates high correlation) Illusionary Correlations – the perception of a relationship where none exist. Comes from a need to make sense of the world Vivid experiences/cases stand out

SCATTERPLOTS + 1.00 - 1.00 0.00 Perfect positive correlation Perfect negative correlation No relationship, no correlation + 1.00 - 1.00 0.00 Click to reveal bullets and example. Click again to reveal answers.

If self-esteem correlates with depression, there are still numerous possible causal links: No animation.

When the number of absences increases, students’ grades tend to decrease As we get older our income tends to increase Adolescents who eat dinner with the family are less likely to do drugs. There tends to be more cavities in people who eat a lot of candy. There tends to be more stress in people with high blood pressure As the number of hours you practice baseball increase, the number of errors decrease. The hotter it is out side the higher the energy bills Which of the following correlation coefficients has the weakest strength?: -.99 .56 .13 -.14 .79 -.38

experimentation Experiment – research method in which an investigator manipulates one or more factors to observe the effect on some behavior or mental process. Controlled procedure aimed to determine cause and effect Controlled through random assignment – assigning participants to experimental and control groups by chance, thus minimizing preexisting differences between the different groups. Experimental group – the group that receives the independent variable (gets the treatment) Control group – used as a comparison, does not receive the independent variable.

Experimentation hypothesis example: playing video games lowers concentration levels Independent variable – the experimental factor that is manipulated; the variable whose effect is being studied. (video games) Dependent variable – the outcome factor; the variable that may change in response to manipulations of the independent variable. (concentration levels) Confounding Variables – a factor other than the independent variable that might produce an effect in an experiment. (preexisting concentration levels)

Experimentation Placebo effect - experimental effects that are caused by expectation about the intervention. placebo – an inactive substance or other fake treatment in place of the experimental treatment. (blindly given to control group) Single-blind – participants do not know whether they are in experimental or control group double-blind – neither participants nor research staff knows which participants are in the experimental or control groups. This eliminates experimenter bias as well. An experiment has validity if it tests what it is supposed to test.