basic issues in experimental research

basic issues in experimental research

1. manipulating the independent variable

   • types of independent variables
     • environmental manipulations
       • involve experimental modifications of aspects of the research setting
     • confederates
       • accomplices of the serearcher who pose as other participants or as uninvolved bystanders
     • instructional manipulations
       • vary the independent variable through instructions or information that participants receive
     • invasive manipulations
       • involve creating physical changes in the participant's body through physical stimulation (such as in studies of pain)
   • experimental and control groups
     • experimental groups
       • participants who receive a nonzero level of the independent variable
     • control groups
       • those who receive a zero level of the independent varibale
   • assessing the impact of independent variables
     • pilot test
     • manipulation check
       • question (or set of questions) that is designed to determine whether the independent variable was manipulated succesfully
   • independent variables versus subject variables
     • subject or participant variables

2. dependent variables

   • a dependent variable is the response being measured in the study

3. assigning participants to conditions

   • simple random assignment
     • involves placing participants in conditions in such a way that every participant has a equal probability of being placed in any experimental condition
   • matched random assignment
     • the researcher obtains participants scores on a measure known to be relevant to the outcome of the experiment
   • repeated measures designs
     • randomized group design / between-subject design
       • participants are assigned to each of the conditions in an experiment
     • within-subjects design
       • in which we are interested in differences in behavior across conditions within a single group of participants

4. Experimental Control

   • systematic variance
   • confound variance
   • treatment variance
   • error variance

5. eliminating confounds

   • biased assignment
     • selection threat to internal validity
   • internal validity
     • the degree to which a researcher draws accurate conclusions about the effects of the independent variable
   • attrition
     • refers to the loss of participants during the study
     • differential attrition
       • when the rate of attrition differs across the experimental conditions
   • pretest sensitization
     • when this occurs, the researcher may conclude that the independent variable has an effect when, in reality, the effect is influenced by the pretest
   • experimenter expectancy effect
   • demand characteristics
     • are aspects of a study that indicate to participants how they should behave
   • placebo
     • placebo control group
   • double-bind procedure
     • enither the participants nor the experimenters who interact with them know which experimental condition a participant is in at the time the study is conducted

6. Error Variance

   • transient states
   • environmental factors
   • differential treatment
   • measurement error