Within Subjects Design - Research Methods in Psychology/Social Sciences
Summary
TLDRThis educational video delves into the within-subjects experimental design, contrasting it with the between-subjects design. It explains the use of the same group of participants across different conditions, highlighting its advantages such as controlling for individual differences and requiring fewer participants. The script also addresses potential threats to internal validity, like environmental changes, time-related variables, and order effects, and suggests strategies like counterbalancing and pilot testing to mitigate these issues. It concludes with guidance on choosing between within-subjects and between-subjects designs based on factors like individual differences, treatment effects, and participant availability.
Takeaways
- 🔍 The within-subjects design involves the same group of participants being tested or observed under all different conditions of an experiment.
- 📚 A key advantage of within-subjects design is that it allows for the ultimate control of extraneous variables by reusing the same participants across conditions.
- 🕵️♂️ The study by Stephens et al. (2009) demonstrated that swearing can help individuals tolerate pain more effectively, illustrating the application of within-subjects design.
- 🧠 Schmidt's (1994) research on word recall showed that humorous sentences are more memorable than neutral ones, another example of within-subjects design.
- ⏱️ Time-related confounding variables, such as fatigue and practice effects, can influence the results in within-subjects designs where conditions are administered at different times.
- 🌡️ Environmental variables like room size or temperature can confound results if they change between conditions within a within-subjects design.
- 🔄 Order effects, such as carryover effects from one condition to another, can bias results in within-subjects designs if not properly controlled.
- 🔄 Counterbalancing the order of treatment conditions is a technique used to control for order effects in within-subjects designs.
- 👥 Within-subjects design requires fewer participants compared to between-subjects design, making it more efficient in terms of resources.
- ⚖️ The decision between using within-subjects or between-subjects design should be based on factors like anticipated individual differences, potential long-lasting treatment effects, and ease of participant recruitment.
Q & A
What is a within-subjects design in experimental psychology?
-A within-subjects design is an experimental approach where the same group of participants is tested or observed under all the different conditions being compared. This design allows for each individual's performance to be compared across various conditions, making the group synonymous with conditions.
Why might a researcher choose a within-subjects design over a between-subjects design?
-A researcher might choose a within-subjects design to control for individual differences, as each participant serves as their own control by being exposed to all conditions. This design is also advantageous when the number of available participants is limited.
What was the main finding of the study by Stephens and colleagues in 2009 on swearing and pain tolerance?
-The study found that swearing or cursing can make it easier for individuals to tolerate pain, suggesting that expressing emotions through swear words can help people cope with discomfort.
How did Schmidt's 1994 study differ from the study by Stephens and colleagues in terms of within-subjects design?
-Schmidt's study alternated between funny and neutral words, administering all treatments together, while Stephens and colleagues had a time gap between the neutral word and swear word conditions, exposing participants to one condition at a time.
What are the potential threats to internal validity in a within-subjects design?
-Threats to internal validity in a within-subjects design include confounding from environmental variables, time-related confounding variables, history, maturation, instrumentation, regression towards the mean, and order effects.
What is the concept of 'counterbalancing' in the context of within-subjects designs?
-Counterbalancing is a technique used to control order effects by changing the order in which treatment conditions are administered across different participants, ensuring that the order of conditions does not influence the study's results.
Why might a within-subjects design require fewer participants compared to a between-subjects design?
-A within-subjects design requires fewer participants because the same individuals are tested under all conditions, eliminating the need to recruit separate groups for each condition, thus saving time and resources.
What are some strategies to mitigate the effects of practice and fatigue in a within-subjects design?
-Strategies to mitigate practice and fatigue effects include conducting pilot tests to understand their impact, shortening the duration of the experiment, and considering alternative designs such as between-subjects if within-subjects design poses too many challenges.
How can a researcher determine whether to use a within-subjects or a between-subjects design for their study?
-A researcher can determine the appropriate design by considering factors such as anticipated individual differences, potential long-lasting effects of treatments, ease of recruiting participants, and the specific requirements and goals of their study.
What are the advantages and disadvantages of using a within-subjects design?
-Advantages include controlling for individual differences and requiring fewer participants. Disadvantages include potential practice effects, fatigue, mortality (participant dropout), and the need for participant commitment over an extended period.
Outlines
🔍 Introduction to Within-Subjects Design
The paragraph introduces the concept of within-subjects design, contrasting it with between-subjects design. In within-subjects design, the same group of participants is tested under different conditions, unlike between-subjects design where different groups are compared. The paragraph explains that this design allows for each participant to serve as their own control, reducing the influence of individual differences. It also provides an example of a study by Stephens et al. (2009) that examined the effect of swearing on pain tolerance, illustrating how within-subjects design can be used to establish cause-and-effect relationships by manipulating one variable (swearing) while controlling for others (same participants across conditions).
🕒 Time and Environmental Factors in Within-Subjects Design
This section delves into the potential threats to internal validity in within-subjects design, particularly focusing on time-related and environmental confounding variables. It discusses how changes in the environment between conditions can affect the outcome, emphasizing the need for consistency. The paragraph also addresses the issue of time, explaining how factors like fatigue, maturation, and history can influence participant performance and obscure the effect of the experimental manipulation. The discussion serves as a cautionary note on the careful planning required to conduct a within-subjects study effectively.
📊 Understanding Order Effects and Other Challenges
The paragraph explores the concept of order effects in within-subjects design, where the sequence of conditions can influence participant responses. It explains phenomena like fatigue, practice effects, and carryover effects, which can occur when the same participants are tested multiple times. The text provides an example to illustrate how the order of treatments can lead to improved performance not due to the treatment itself but because of the lingering effects of previous treatments. The paragraph also touches on the strategy of counterbalancing to mitigate order effects by varying the order of conditions across different participants.
📉 Balancing Time Span and Participant Commitment
This section offers strategies for managing the challenges associated with the time span of experiments in within-subjects design. It suggests conducting pilot tests to understand the impact of practice and external events on results and considering the balance between a long and short experimental timeline. The paragraph also discusses the option of switching to a between-subjects design if within-subjects design poses too many complications. Additionally, it mentions the advantage of within-subjects design in requiring fewer participants and the potential issue of participant dropout, or mortality, which can skew results if not managed properly.
📚 Choosing Between Within-Subjects and Between-Subjects Designs
The final paragraph provides guidance on choosing between within-subjects and between-subjects designs. It outlines scenarios where each design might be preferable, such as when individual differences are expected to be significant, when treatments are expected to have lasting effects, or when participant recruitment is challenging. The paragraph also discusses the applications of within-subjects design, including simple two-condition studies and multiple treatment designs, while acknowledging the challenges of maintaining participant commitment over an extended period. It concludes by emphasizing the importance of careful consideration in selecting an experimental design.
Mindmap
Keywords
💡Within-Subjects Design
💡Between-Subjects Design
💡Internal Validity
💡Confounding Variables
💡Time-Related Confounding Variables
💡Order Effects
💡Counterbalancing
💡Practice Effects
💡Fatigue Effects
💡Carryover Effects
💡Mortality
Highlights
Introduction to within-subjects design, contrasting it with between-subjects design.
Explanation of within-subjects design where the same group is used across different conditions.
Example of a study by Stephens et al. (2009) on the effects of swearing on pain tolerance.
Findings from Stephens et al. that swearing can help tolerate pain.
Schmidt's (1994) study on memory retention of humorous versus non-humorous words.
Advantage of within-subjects design in matching participants by reusing the same group.
Difference between methodologies of Smith and Schmidt in handling treatment conditions.
Threats to internal validity in within-subjects design, such as environmental variables and time-related variables.
Discussion on history, maturation, and instrumentation as time-related confounding variables.
Explaining regression towards the mean as a potential threat in within-subjects design.
Order effects and their impact on experimental results.
Strategies to control for order effects, such as counterbalancing.
Advantages of within-subjects design, including fewer required participants and elimination of individual differences.
Limitations of within-subjects design, such as practice effects, fatigue, and participant mortality.
Guidelines for choosing between within-subjects and between-subjects designs based on anticipated effects and participant availability.
Applications of within-subjects design in evaluating two or more conditions with the same participants.
Conclusion and summary of key points regarding within-subjects design.
Transcripts
hello everyone for today we are going to
talk about another type of experimental
design
and this time we are going to discuss
the within subjects design
so if you remember our last discussion
we talk about between subjects design
and in between subjects design
you learn that we compare two groups or
more
and the participants in these groups
should not be the same but rather there
are different participants
for every group this time you will learn
that it's also possible
for us to conduct an experiment by using
the same group
again and again and that's why it's
called within
subjects design so even though you have
different conditions
you still use the same group that's why
group
is not synonymous with conditions all
the time in experimental
psychology so let's begin
so the characteristic of a within
subject's design is that
it uses a single group of participants
and tests
or observes each individual in all the
different treatments being compared
so instead of recruiting other
participants in order for you to compare
one group or one condition to another
what you're doing here is that you're
exposing the same group to a lot of
different conditions
to conditions recondition so on and so
forth and then you compare their
performance
in these different conditions let's try
to know
why is there a need for such approach in
designing an experiment
here is an example of a study that
utilized a within subjects design
so stephens and colleague back in 2009
examined the effects of swearing on the
experience of pain
so what they did is that in one
condition the participants were told to
repeat their favorite swear word
over and over for as long as their hands
were in the water
you may be asking right now why is there
a need for the participant to put his
hand in the water
it's because that's the safest way to
induce
pain and this is cold water and
if your hand is immersed on cold water
for a long time that's
painful in the second condition the
participants repeated
a neutral word so in other words you
were told to
put your hands on icy water then at the
first condition you will
repeat your favorite curse word or swear
word
and then in the second condition you
will say a neutral word for example
rabbit
they found out if you swear or if you
curse
it's easier for you to tolerate pain
that's why there are people who are
cursing
when they are in pain so they were able
to prove that it's easier for people to
cope
when they express their emotions
especially
when they say swear words let's look at
another example
in this example sm schmidt in 1994
investigated what types of words can we
recall and the way that he delivered the
sentence is deeper
is it funny is it humorous or
non-humorous or not funny
and then he asks them to recall as many
as possible
so in other words it's a non-funny word
followed by a funny word followed by
another non-funny word
so on and so forth he discovered
eventually that people are
more likely to remember funny sentences
over neutral sentences both
studies utilize a within subject's
design
but what is the difference
later you will know more about that but
now let's talk more about
the within subjects design so the key
element of a within subjects design is
that
all the individuals in one sample
participate in all the treatment
conditions
so you participate more than once and if
you take a look at it
your performance in one condition is
being compared to your performance
to the previous condition or to the next
condition
other than that a within subject study
is the ultimate
and equivalent groups because the group
in one treatment condition
is absolutely identical to the group in
every other condition
that may be a little complex so let me
explain it
do you remember that back in between
subjects design
we need to match the participants or to
find a group that's
very similar to the group that we have
so that there will be little extraneous
variables but come to think of it
instead of matching groups why don't we
recruit the same group or make use of
the same group
in another condition because technically
that is the ultimate way or the best way
to match participants in other words the
best way to match
groups is to reuse your participants
you don't have to worry about matching
anymore because by using the same
participants
you are already matching so that's one
advantage
of a within subjects design so here's
the difference
between the studies of smith and
colleagues and stephens and colleagues
and in stephens and colleagues case they
utilize letter a
they recruited a sample they exposed
them to treatment condition one
which is the neutral word and then after
that
they rested for a little while and then
they were exposed to condition too
which is the swear word condition in
letter a
the treatments are not being
administered
at the same time but there's a time
difference there's a gap
between one treatment condition to
another
on the other hand the methodology used
by schmidt
made use of letter b because he
alternated funny
with neutral words so in other words all
the treatment
all the treatments were administered
together
in my personal experience it's easier to
find something that follows letter a
than letter b in this lecture you will
learn about
the weaknesses of the within subjects
design but at the same time
you will learn about its advantages so
you
you will also learn when should you
utilize a between groups design
and when should you utilize a within
subjects design
now that you have a basic idea about the
characteristics of a within subject's
design
it's time to talk about the threats to
internal validity and in order for us to
talk about this in detail
first let me remind you of the meaning
of internal validity
so if there's internal validity and
research this is the extent to which a
research study
produces a single unambiguous
explanation
for the relationship between two
variables or if i'm going to state it in
my own words
you achieve what we call internal
validity if
you have you were able to establish
cause and effect and
this relationship is not due to external
factors or to extraneous variables
another way to say it is that you are
sure that the changes in the dv
is caused by the changes in the iv
now let's look at the possible threats
in establishing cost and effect
relationships
when it comes to within subjects design
so let's begin
first we have what we call confounding
from environmental variables
when we say environmental variables
these are characteristics of the
environment
that may change from one treatment
condition to another
so even though you use the same
participant more than once
make sure that the environment where you
conducted your research
are very similar if not the same
so you cannot use a bigger room in the
next condition
especially if the one you use in the
previous condition is a small room
you cannot expose them to a warm room if
previously
the room was cold especially if your
experiment
is not about temperature you cannot make
use of a dark room
if your experiment is supposed to be
conducted in a well-lit
room so these are environmental
variables
even though you are using the same set
of participants
these environmental variables become
extraneous factors
that hinder internal validity or
make it challenging to establish cause
and effect
other than that there can be time
related
confounding variables so this is a
serious concern in within subjects
design
that comes from the fact that the sign
often requires a series of measurements
made over time so an example if i'm
going to tell you that
for the second condition i need you to
return by the afternoon
then the problem is that maybe you are
more tired in the afternoon
answer performance later today will not
be the same with your performance now
so the change in your performance is not
due to the manipulation
but it's due to time related elements
what if i tell you that i want you to
come back after
one month for the second part of the
experiment but
a lot can happen in one month and the
changes that we observe
may not come from the experiment but
rather it may come from time related
elements
what are these time-related elements
first we have what we call history
or the events that occur in the
participants personal lives
what if one of your participants get
married what if one of them had a
problem
what if one of them graduated from
college then these
are significant events in one's life
and these are things that are beyond our
control
they will change the well-being of your
participant and that will influence
the way your participant answer the way
your participant performs
during the study so that's for history
we also have maturation so the longer
that you make them participate in your
experiment
there's a possibility for them to mature
as well
there may be physiological or
psychological changes
that occur in participants during the
study
and influences the participants scores
for example our research is about test
taking
skills i would like to expose you
to different brain enhancing vitamins
and i would like to take the test
afterwards however the more tests that
you take
the better you are are test taking
what if in the last condition you are
now very good in taking tests
i might conclude that because of the
last vitamin i have given you
you had an improvement in test taking
strategies
however the improvement is not due to
the brain enhancing vitamin
but rather it's because there's what we
call
maturation or there were psychological
changes
in the span of his participation we also
have what we call
instrumentation or changes in a
measuring instrument
that occur over time an example
in the first day of an experiment i
observed your aggressive behavior
i saw you kick another kid in the room
then i'm going to rate that behavior as
very aggressive
however since i am in that observation
room for every day of my life
i see a kid kick someone else every day
then after one month the same behavior
may not be rated in the same way after
one month
what i initially considered as extreme
may now be considered
average i may have experienced some
changes
in the way that i rate behaviors and
that's
those are the changes in instrumentation
we also have what we call regression
towards the mean
or the average which means that
for every extreme score there's a
tendency
to move towards the mean an example
because you're so intelligent you got a
high score in my experiment
however you cannot perform excellently
all the time
the more tests that you take there's a
possibility that your score will go
closer to the average that's what we
call regression towards the mean
sometimes high scorers become average or
sometimes
low scorers become average as well
that's another phenomenon that happens
in within subjects
design we also have what we call order
effects or
the way that we order our manipulation
remember my example before about the
books let's reuse the example
read book one and then take test one
after one week read book two then take
test
2. then you found out that participants
scored better
after taking test 2 however
it may not be due to the book that they
use but rather
perhaps it's because that person can
still remember
what he learned back in book one hence
there were some carry over
effects the high scores cannot be
attributed
to the type of book that was used but
rather
because the way that the manipulations
are ordered they are now
carrying over to other manipulations
so the more book that you read the more
intelligent that you
become that's why sometimes we also have
to change
the order of our manipulations so that
the changes in scores
will not be explained by order effects
and what are the examples of order
effects number one we have what we call
fatigue
or the more books that you read perhaps
you will decline in your performance
because you will be tired
or we also have what we call practice
the more tests that you take
the better you are in test taking
so these are two concepts related to
order effects
we also have what we call carryover
effects which is actually related to
practice effect
so there may be some sort of rehearsal
the more that you take the same
manipulation
the better you are in understanding the
goal of the experiment that's why
your performance turned out to be better
taking one test after another
will make you a better test taker here's
an example
of the effects of order effect on the
left side this
is these are scores with no order
effects
ideally there should be no carryover
effects to the other condition
but if you look at the second condition
in group b
look at this in treatment 2 all of them
got a plus
5 in their scores why it's because
in treatment 2 they can still remember
what they learned from
treatment 1. that's why their experience
in treatment one
is carrying over to treatment too
in other words even though right now
what we are measuring is your ability to
take the test after reading book 2
you can still remember what you read
back in book 1
and that influences your performance
after reading book 2. that's why there
was an increase in scores
after the second treatment
now let's talk about what we can do in
order for us these different sources of
error
and experimentation the first thing that
you can do
is controlling time if there's a problem
with the time span of the study then
let's try to conclude it for example
if the different treatment conditions
are scheduled over a period of weeks
the chance has greatly increased that an
outside event maturation
or change in the measurement instrument
will have an influence
on the results so what we can do is that
we can try to shorten the span of the
experiment
for example if instead of doing that for
three weeks
let's try to do it in three days however
if you do it that way there's another
threat and what is that
practice effect or fatigue that's why
you need to find a balance
between stretching your experiment or
compressing your schedule
because the longer the time span of your
experiment the greater the possibility
that there are outside factors but the
shorter your time span
then there's a higher possibility for
practice effects
so what is my advice i hope that you'll
be able to conduct
a pilot testing first so that ahead of
time you will know
how can practice effect and how can
external events
affect the results of your experiment
also if with if a within subject design
will cause a lot of problem
then you can simply switch to a between
subject's design
usually between subjects design the one
with separate groups
is available as an alternative and
completely eliminates
any threat of confounding from order
effects
however when you switch from within
groups to between groups
then you're going to have to deal with
new problems and what are those
you will have to deal with the problems
that we talked about in the previous
lecture
such as matching randomization and
other things also if there are problems
when it comes to order effects
you can apply what we call
counterbalancing i think i've
already mentioned to you what counter
balancing is so counter balancing is
defined as changing the order in which
treatment conditions are administered
from one participant to another so the
treatment conditions are matched with
respect to time
example earlier in this lecture
participants were asked to say
either neutral or curse words but in
that experiment
they counter balance the treatment by
changing the order
some participants were told to say
neutral words
first while some other participants were
told to
say curse words first so that
the order of the conditions will not
affect the results of the study
what are the limitations of
counterbalancing with only two treatment
conditions
complete counter balancing is easy it's
easy for you to order the manipulation
in a way
that you will reduce order effects and
there are only two possible sequences
however as the number of treatments
increases
complete counterbalancing will become
more complex
say for example what if you have eight
treatments rock music
pop music classical music then
you're going to make one person hear
all those types of music if you're going
to do that to a lot of participants then
you have to get
all possible combinations in order for
you to completely counterbalance
the order of your manipulation and that
takes a lot
of time sometimes you might consider
limiting your manipulations
so that it will be easier to do counter
balancing
now let's talk about the advantages of a
within subjects design one advantage is
that it requires
relatively few participants in
comparison to between subjects design
and why is that
in between subjects design if you have
three conditions with 30 participants
each
you need 90 participants but in a within
subject design and you have three
conditions
you can reuse the same participants
that's why instead of needing 90
you can only make use of 30 participants
and that saves a lot of time
and effort it essentially eliminates all
the problems based on individual
differences
that are the primary concern of between
subjects design
remember last time we talk about the
influence of individual differences
that is being eliminated when we do a
within subject design however
when you make use of within subjects
design you will encounter new problems
such as practice
and fatigue and other things
other than that you might encounter what
we call mortality
or because you're using the same
participants again and again and what if
you need their participation for eight
weeks
some participants who start the research
study
may be gone before the study is
completed they may drop out they may
quit
hence your group will your group will
not be the same
as when you started the experiment
that's why
this will influence how you make
conclusions because most of the time
the participants who are going to stay
are those who have very high commitment
that is also a factor in making
conclusions because right now
personality is having an influence on
your
results now how do you know if you're
going to use a within subject design
or a between subjects design look at
these three
scenarios so if you anticipate large
individual differences
perhaps it's better to use within
subjects design
so you will know it sometimes before you
decide and decide on conducting
experiments you try to read the
literature
try to determine if individual
differences will be a big factor
in that study other than that whenever
you expect one or more treatment
conditions to have a large
and long-lasting effects that may
influence the participants in the future
conditions
meaning there can be practice effect or
fatigue effects
order effects then it's better to use a
between subject design for example
if your experiment is about test taking
or it's about teaching
perhaps a within subjects design is not
the best
it's not the best approach because if
you use teaching as manipulation
then that's not going to be easily
forgotten
it will be retained even after some time
and lastly whenever it's difficult to
find and recruit participants
a within subject design is a better
choice for example
you want to conduct experience with
people with learning disability
then it might be difficult to find 100
individuals with learning disability
that's why it's better to make use
of a within subject design however the
challenge here is that
you need to get their commitment to
participate in your study
so here are the applications just like
last time a within subject design can be
used in evaluating two conditions but
this time you have same participants so
that's the simplest type
of a within subjects design also you can
make use of multiple treatment designs
or
you can have three or more groups and
multiple treatment designs also produce
a more convincing demonstration of cost
and effect relationships
compared to a two group design the
problem is that
it may be hard to get to get their
commitment for a long period of time
that's why you need to weigh a lot of
issues before choosing
if you're going to make use of it
between subjects or a within
subjects design basically that's what
you need to learn about within subjects
design
and i do hope that you learned a lot
from this discussion
and you need to be more cautious before
deciding
on your experimental design
that's it and i hope you learned a lot
thank you
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