1Relationships Between Relationships Between VariablesVariables Linear relationshipsLinear relationships•• Positive linear relationship.Positive linear relationship. Both variables increase or decrease at the Both variables increase or decrease at the same rate in the same direction.same rate in the same direction.Rtd tiht li i Rtd tiht li i 1212Represented as a straight line going up on a Represented as a straight line going up on a graphgraph•• Negative linear relationshipNegative linear relationship As one variable increases the other variable As one variable increases the other variable decreases at the same rate.decreases at the same rate. Represented as a straight line going down Represented as a straight line going down on a graphon a graphLinear Relationship GraphsLinear Relationship GraphsPositivePositive NegativeNegative1313Relationships Between Relationships Between VariablesVariables Curvilinear relationshipCurvilinear relationship•• As one variable increases the other variable As one variable increases the other variable both increases and decreases over time both increases and decreases over time (nonmonotonic).(nonmonotonic).1414•• RepresentedRepresented as a curved line on a graph.as a curved line on a graph. No Relationship between variable No Relationship between variable changeschanges•• Represented by a flat, horizontal line on a Represented by a flat, horizontal line on a graph.graph.Curvilinear Relationship GraphCurvilinear Relationship Graph1515A researcher measured how much violent television A researcher measured how much violent television children watched at home. These children were also children watched at home. These children were also observed for their aggressiveness on the playground. The observed for their aggressiveness on the playground. The researcher found that as the amount of violence watched researcher found that as the amount of violence watched on TV increased, the amount of playground on TV increased, the amount of playground aggressiveness increased. The type of relationship found aggressiveness increased. The type of relationship found waswasA.A. negative linear.negative linear.B.B. positive linear.positive linear.C.C. curvilinear.curvilinear.D.D. none of thesenone of these1616The finding that a person’s shoe size is not associated with The finding that a person’s shoe size is not associated with their family income suggests what type of relationship?their family income suggests what type of relationship?A.A. negative linear.negative linear.B.B. positive linear.positive linear.C.C. curvilinear.curvilinear.D.D. none of thesenone of these17172Dr. Kramer found that the average number of miles driven Dr. Kramer found that the average number of miles driven decreases as the price of gasoline increases. This decreases as the price of gasoline increases. This relationship can best be described as a _______ relationship can best be described as a _______ relationship.relationship.A.A. negative linear.negative linear.B.B. positive linear.positive linear.C.C. curvilinear.curvilinear.D.D. none of thesenone of these1818A researcher finds that the more a song is played on the A researcher finds that the more a song is played on the radio, the greater the liking for the song. However, she radio, the greater the liking for the song. However, she also finds that if the song is played too much, people start also finds that if the song is played too much, people start to dislike the song. What type of relationship does this to dislike the song. What type of relationship does this represent?represent?A.A. negative linear.negative linear.B.B. positive linear.positive linear.C.C. curvilinear.curvilinear.D.D. none of thesenone of these1919Experimental vs. Experimental vs. NonexperimentalNonexperimental MethodsMethods Nonexperimental methods simply measure Nonexperimental methods simply measure the variables of interest in an attempt to the variables of interest in an attempt to discover a relationship between them (if discover a relationship between them (if th i l ti b t th )th i l ti b t th )2020there is a correlation between them).there is a correlation between them). Experimental methods Experimental methods systematically systematically changechange some variables and measure the some variables and measure the effects of these changes on other effects of these changes on other variables to assess the relationship variables to assess the relationship between them. between them. NonexperimentalNonexperimental MethodsMethods These methods are good for discovering if These methods are good for discovering if two or more variables two or more variables covarycovary..•• CovariationCovariation or correlation is useful for or correlation is useful for prediction (if you know the value of one prediction (if you know the value of one i bl di t th l f l t d i bl di t th l f l t d 2121variable you can predict the value of correlated variable you can predict the value of correlated variable.variable. Examples: High SAT scores are positively Examples: High SAT scores are positively correlated with success in college, seat correlated with success in college, seat belt use is negatively correlated with belt use is negatively correlated with severe injury in auto accidents.severe injury in auto accidents.NonexperimentalNonexperimental MethodsMethods Causality Causality MUST NOT MUST NOT be inferred from be inferred from correlational methodscorrelational methods•• The problem of determining the The problem of determining the direction of cause and effectdirection of cause and effect2222direction of cause and effect.direction of cause and effect. Which change came first?Which change came first?••The thirdThe third--variable problemvariable problem Did some other variable produce the Did some other variable produce the changes in the two measured variables?changes in the two measured variables?Experimental MethodsExperimental Methods Experimental methods introduce Experimental methods introduce techniques of control that allow inferences techniques of control that allow inferences of causality.of causality.•• Extraneous variables are held constant and/or Extraneous variables are held constant and/or their effects are randomized across their effects are randomized across 2323their effects are