Monday, November 21, 2016

Chapter 3: Threats to Validity: external validity – quantitative and mixed methods studies

The threats to validity section in the quantitative and mixed methods checklist is one of the trickiest to understand. Let's see if I can make some sense of it for you. It begins with threats to external validity. External validity is the extent to which the researcher can conclude that results apply to a larger population (generalizability). Here are some common threats to external validity.

•Reactive or interaction effect of testing--a pretest might increase or decrease a subject's sensitivity or responsiveness to the experimental variable. Therefore, giving a pretest changes your participants, they will respond differently later because they took the pretest.

•Interaction effects of selection biases and the experimental variable. You may unintentionally choose people that have particular biases. For example if you are doing an online survey about use of the internet- you will only have people participate who are already comfortable enough with the computer and internet to choose to participate in an online survey. You will be missing people who are not comfortable with computers.

•Reactive effects of experimental arrangements--it is difficult to generalize to non-experimental settings if the effect was attributable to the experimental arrangement of the research. So, if you are doing some type of experiment in a controlled setting (picture a quiet psychology lab room), there is no way to know what will happen when a similar occasion occurs in the real world.

•Multiple treatment interference--as multiple treatments are given to the same subjects, it is difficult to control for the effects of prior treatments. People cannot "unlearn" something, so whatever has happened to them previously will affect future learning/ experiences.

In this section of chapter 3, you need to think through what are the threats to external validity in your study. Keep in mind that no study is perfect, it is ok, in fact, it is expected that there will be issues. The important thing is that you recognize them.

Next time, we will look at threats to validity- internal validity quant and mixed methods. Do you have an issue or a question that you would like me to discuss in a future post? Would you like to be a guest writer? Send me your ideas! leann.stadtlander@waldenu.edu


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