SOLVED

6) Compare and contrast interrupted and equivalent time series designs. What is common to both of them? What is unique to each of them? How do interrupted and equivalent time series designs differ from pre-experimental designs? 7) Diagram the design notation for a classical experimental design. What do each of the symbols represent? 8) In experimental research, what does internal validity refer to? Provide and briefly describe three examples where internal validity is an issue. Answer ?Internal validity refers to the ability to eliminate alternative explanations of the dependent variable—variables, other than the treatment variable(s), that affect the dependent variable are threats to internal validity. These variables threaten the researcher’s ability to say that the treatment was the true causal factor producing change in the dependent variable ?Selection bias is the threat that research participants will not form equivalent groups. ?History effects refer to the threat that an event unrelated to the treatment will occur during the experiment and influence the dependent variable. ?Maturation is the threat that some biological, psychological, or emotional process within the subjects and separate from the treatment will change over time. ?Testing effect threatens internal validity because more than the treatment alone affects the dependent variable. ?Instrumentation occurs when the dependent variable measures changes during the experiment. ?Statistical regression refers to a problem of extreme values or a tendency for random errors to move group results toward the average. ?Mortality arises when some subjects in the experiment leave the experiment before it is concluded. ?Diffusion of treatment is the threat that research participants in different groups will communicate with each other and learn about the other’s treatment. ?Experimenter expectancy threatens internal validity whereby the experimenter indirectly communicates the desired findings to subjects. 9) In experimental research, what does external validity refer to? Briefly describe two instances where external validity is a threat to the overall findings and conclusions of an experiment. 10) Identify and describe three practical issues that all experimenters should be aware of.