Chapter Nine Introduction to Simple Experiments Exam 3 Research Methods Independent variable the manipulated variable experimenter has some independence in assigning people to different levels of this variable Condition levels of variable Dependent variable measured variable how a participants acts on the measured Control variable any variable that an experimenter holds constant on purpose Control group level of independent variable that is intended to represent no variable depends on the level of the independent variable Confounds threats to internal validity confusion to what is causing change in the treatment or a neural condition Treatment group other level of the independent variable in a study that has a control group Placebo group when control group is exposed to an inert treatment such as a sugar pill dependent variable Systematic variability ex Did surly experimenters work only with the red ink group and the sweet ones only with the green and black ink groups design confound Unsystematic variability random or haphazard across all three ink colors then temperament would not be a confound Selection effect when kinds of participants at one level of the independent variable are systematically different from the kinds of participants at the other level of the independent variable related to types of participants placed in each level of the independence variable Random assignment avoids selection effect Matched groups design experimental design in which participants who are similar on some measured variable are grouped into sets and the members of each matched set are then randomly assigned to experimental conditions used for when samples are on the small side Independent groups design different groups of participants are placed into different levels of the independent variable also called between subjects design or between groups design each participant is presented with all levels of the independent design Posttest only design one of simplest independent group experimental designs where participants are randomly assigned to independent variable groups and are tested on the dependent variable once Pretest posttest designs participants are randomly assigned to at least two groups and are tested on the key dependent variable twice once before and once after exposure to independent variable exposed to all the levels of an independent variable at roughly the same time and a single attitudinal or behavioral preference is the dependent measure ex Coke and Pepsi and indicating which they prefer Repeated measures deigns within groups design in which participants are measured on a dependent variable more than once that is after exposure to each level of the independent variable Power within groups designs give researchers more power to notice differences between conditions statistically speaking when extraneous differences unsystematic variability in personality sex ability etc are held constant across all conditions researchers will be more likely to detect an effect of the independent variable manipulation power is ability of sample to show a statistically significant result when something is truly going on in the population confound meaning that participants performance at later levels of the independent Within groups design within subjects design only one group of participants and Order effects or carryover effects an order effect in a within groups design is a Concurrent measures design within groups design in which participants are Counterbalancing used to avoid order effects they present the levels of the variable might be caused not by the experimental manipulation but rather by the sequence in which the conditions were experienced independent variable to participants in different orders Partial counterbalancing only some of the possible condition orders are represented two ways to do it is to present conditions in a randomized order for each subject or to use a Latin square Latin square formal system of partial counterbalancing that ensures that each condition appears in each position at least once Demand characteristics experimental demand when an experiment contains cues that lead participants to guess its hypotheses Pilot study simple study using a separate group of participants that is completed before or sometimes after the study of primary interest in conducted used to confirm the effectiveness of their manipulation Manipulation checks used by researchers to collect empirical data on the construct validity of their independent variables an extra independent variable that researchers can insert into an experiment to help them quantify how well an experimental manipulation worked they related Pgs 246 247 Dependent variable is the measured variable how a participant acts on the 1 What is an independent variable dependent variable and control variable How are Independent variable is the manipulated variable coming from the fact that the researcher has some independence in assigning people to different levels of this variable measured variable depends on the level of the independent variable researchers have less control over the dependent variable Independent variable almost always on the x axis dependent variable almost always on the y axis Control variable any variable that an experimenter holds constant on purpose allow researchers to separate one potential cause from another and thus eliminate alternative explanations for results They have covariance temporal precedence and internal validity because every independent variable has at least two levels experiments always are set up to look for covariance comparison groups treatment groups control groups Experiments establish temporal precedence by manipulating the causal variable to ensure it came first in time different from correlation study which is a snapshot Internal validity matched group designs and random assignment avoid selection effects Covariance because experiments manipulate an independent variable and 2 Why can experiments make causal claims Pg 247 Design confound a second variable that happens to vary systematically along 3 What is a design confound Give two of your own examples Pgs 249 250 with the intended independent variable and therefore is an alternative explanation for the results Threat to internal validity 4 What is the difference between systematic and unsystematic variability Which is more of a threat to internal validity Pg 250 Unsystematic variability is not a design confound and the only
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