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, in honor of Christmas, we will have a guest
writer, Dr. Susan Ruiz. She is a recent Walden grad who will share with you
some of her experiences. 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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