Psych Reading for January 14th Page 55 72 Correlational Designs Correlational Design Research design that examines the extent to which two variables are associated If two things are correlated they relate to each other Correlations can be positive zero or negative o Positive As the value of one variable changes the other goes in the same direction o Zero The variables don t go together o Negative As the value of one variable changes the other goes in the opposite direction Correlation coefficients range in value from 1 0 to 1 0 o 1 0 is a perfect negative correlation o 1 0 is a perfect positive correlation o Values lower than 1 0 indicate a less than perfect correlation coefficient Scatterplot A grouping of points on a two dimensional graph in which each dot represents a single person s data Illusory Correlation The perception of a statistical association between two variables where none exists Experimental designs permit cause and effect inferences In correlational designs the differences among participants are measures whereas in experimental designs they re created An experiment consists of two ingredients o Random assignment of participants to conditions Random Assignment The experimenter randomly sorts participants into one of two groups Experimental Group Receives the manipulation Control Group Doesn t receive the manipulation Random selection deals with how we initially choose our participants whereas random assignment deals with how we assign our participants after we ve already chosen them o Manipulation of an independent variable Independent Variable The variable the experimenter manipulates Dependent Variable The variable that the experimenter measures to see whether this manipulation has had an effect Operational Definition A scientist s working definition of what they re measuring Confounding Variable Refers to any difference between the experimental and control groups other than the independent variable Placebo Effect Improvement resulting from the mere expectation of improvement Patients must remain blind to the condition to which they ve been assigned Nocebo Effect Harm resulting from the mere expectation of harm Experimenter Expectancy Effect Rosenthal Effect Occurs when researchers hypotheses lead them to unintentionally bias the outcome of a study Double Blind Neither researchers nor participants know who s in the experimental or control group Demand Characteristics Cues that participants pick up from a study that allow them to generate guesses regarding the researcher s hypotheses Ethical Issues in Research Design Informed Consent Informing research participants of what is involved in a study before asking them to participate Debriefing A process whereby researchers inform participants what the study was about Statistics The Language of Psychological Research Statistics The application of mathematics to describing and analyzing data Descriptive Statistics Numerical characterizations that describe data o Central Tendency Measure of the central scores in a data set or where the group tends to cluster Mean Average a measure of central tendency Median Middle score in a data set a measure of central Most frequent score in a data set a measure of central o Variability Measures of how loosely or tightly bunched scores are o Range Difference between the highest and lowest scores a measure tendency tendency of dispersion o Standard Deviation Measure of dispersion that takes into account how far each data point is from the mean Inferential Statistics Mathematical methods that allow us to determine whether we can generalize findings from our sample to the full populations A statistically significant result is believable it s probably a real difference in our sample Practical Significance Real world importance Pages 74 77 Evaluating Psychological Research Consider the source Watch out for excessive sharpening and leveling o Sharpening The tendency to exaggerate the gist or central message of a study o Leveling The tendency to minimize the less central details of a study Can be misled by seemingly balanced coverage of a story o Sometimes causes pseudosymmetry the appearance of a scientific controversy where none exists
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