Continuing from last time on the scientific method
as applied to Psychology.
Hypothesis testing—systematic observations to
determine if observations are consistent with your initial observation…
One of the best ways to test hypotheses, when it is
feasible, involves conducting an experiment.
Let’s take the example from the Shaffer reading regarding the Kim et al.
experiment about prenatal ethanol exposure.
It is only when we use experiments that we are able to make cause-and-effect
conclusions about our hypotheses.s
What was the hypothesis being tested in the Kim et
al. study? Ethanol during gestation
impairs learning.
Important terminology regarding features of an
experiment
independent variable: what was manipulated? Presence of ethanol in diet during gestation. 3 levels of IV: ethanol in diet; pair-fed
controls; normal fed controls
dependent variable: what was measured? Learning
in test of spatial aptitude.
operational definition: how did they define the constructs
under study? Morris Water Maze performance, reduction in
latency to finding platform over repeated days.
ramdom assignment: how did
subjects get put into groups? Randomly assigned pregnant dams to feeding
groups, one adult selected from each litter in adulthood.
Blind: did the experimenter know what group the
subject was in? Experimenters were blind…previous research showed that
experimenters who thought they were testing smart rats recorded better learning
than experimenters who thought they were testing dull rats (both groups of rats
were the same).
confounding
variables (may be associated with design of the independent variables,
assignment to groups, and to the measures under study): how might incorrect
conclusions have been made? How do you prevent that from happening? How did trials 59 and 60
correct for potential confounds?
Trial 59: raised the
platform to eliminate the possibility that group differences weren’t due to
learning, but may have been due to impairments in using the visual information
from around the room (it is these cues that are important in the Morris Water
Maze). If the ethanol- treated rats
showed the same performance as control rats, then it can be concluded that the
treatment did not appear to affect their ability to process visual
information. If the ethanol-treated rats
also showed slower latency to finding the visible platform, then maybe they
have a problem with their vision, not their learning ability.
Trial 60: removed
platform and tested number of times the rats crossed over where the platform
used to be—a measure of persistence. If
the ethanol-treated group gave us sooner, then maybe “learning impairments”
were reflective of changes in motivation level, rather than cognitive deficit.
Overall, the
findings supported the hypothesis that ethanol treatment led to deficits in
cognitive performance.
control
groups/placebo effects: what were the control groups? Why?
not
all systematic studies are “experiments”
correlational approach---can
detect relationships, cannot discern causality
When consistency is obtained the hypothesis becomes
a theory and provides a
coherent set of propositions which explain a class of phenomena. A theory is
then a framework within which observations are explained and predictions are
made. If observations, made more carefully, start to become inconsistent with a
theory, then theory becomes modified.
But when does theory and hypothesis give way to
fact? Science is ostensibly about
"search for truth", but we never really get there do we, since part
of the scientific method leaves room for work to be falsified. We can never prove a theory
correct (logically impossible to provide positive proof)—we can only
provide support for it. Preponderance
of evidence helps to provide strong support—converging lines of research all
coming to similar conclusions…
We can't prove theories correct, because the very
nature of the scientific method allows for falsifiability
(give example of something non-falsifiable).
And failing to find support for a theory may, but
does not necessarily disprove it either, because being wrong may mean that we
didn't observe carefully enough…if one study does not support the hypothesis,
it does not falsify the theory on which the hypothesis is based. However, if many studies fail to support the
hypotheses that derive from a theory, we can begin to question the theory.
So, in scientific research, you will rarely see the term
PROOF—but we as lay people use it all the time, especially in advertising!