Within Subjects Design - Research Methods in Psychology/Social Sciences

Summary

This 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

00:00

🔍 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).

05:01

🕒 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.

10:01

📊 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.

15:04

📉 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.

20:04

📚 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.

Keywords

💡Within-Subjects Design

A within-subjects design, also known as a repeated measures design, is a type of experimental design where the same participants are tested under all conditions of the experiment. This design allows researchers to control for individual differences by using each participant as their own control, thus increasing the statistical power of the study. In the video, the concept is introduced as a contrast to between-subjects design, where different participants are used for different conditions. The video emphasizes how within-subjects design is used when the researcher wants to compare different conditions on the same group of subjects, as illustrated by the example of a study on the effects of swearing on pain tolerance.

💡Between-Subjects Design

Between-subjects design is an experimental design where different groups of participants are used for each condition being tested. This design is useful when the researcher wants to eliminate the potential influence of individual differences on the results. In the video, it is mentioned as the design where participants in different groups should not be the same, which is the opposite of within-subjects design. The video explains that in between-subjects design, the goal is to match participants across groups to control for extraneous variables.

💡Internal Validity

Internal validity refers to the degree to which a study can produce a clear, unambiguous explanation for the relationship between two variables, ensuring that the observed effect is due to the manipulation of the independent variable and not to external factors. The video discusses internal validity in the context of within-subjects design, emphasizing the importance of establishing a cause-and-effect relationship without interference from extraneous variables. It is crucial for researchers to ensure internal validity to make valid conclusions from their experiments.

💡Confounding Variables

Confounding variables are extraneous factors that can affect the outcome of an experiment and make it difficult to determine the true effect of the independent variable. In the video, the speaker mentions environmental variables as a type of confounding variable that can affect internal validity in within-subjects design. An example given is the change in room temperature from one condition to another, which could influence participants' responses independent of the experimental manipulation.

💡Time-Related Confounding Variables

Time-related confounding variables are factors that can influence the results of an experiment due to the passage of time. These can include participant fatigue, maturation, or changes in the measurement instrument. The video provides examples such as participants being more tired in the afternoon or changes in the way an observer rates behavior over time. These variables can obscure the true effects of the experimental manipulations.

💡Order Effects

Order effects occur when the order in which treatments are administered influences the outcome of the experiment. This can happen due to practice effects, fatigue, or carryover effects from one condition to another. The video explains order effects with the example of reading books and then taking tests, where the performance on the second test might be influenced by the memory of the first book read. The video suggests counterbalancing as a method to control for order effects.

💡Counterbalancing

Counterbalancing is a technique used in experimental designs to control for order effects by varying the order of treatment conditions across participants. This helps to ensure that any effects observed are due to the treatments themselves and not the order in which they were received. The video discusses counterbalancing as a solution to the problem of order effects, especially in within-subjects designs where the same participants are exposed to multiple conditions.

💡Practice Effects

Practice effects refer to improvements in performance that occur as a result of repeated exposure to a task or test. In the context of the video, practice effects are mentioned as a potential issue in within-subjects designs, where participants may perform better on later conditions simply because they have become more familiar with the task, rather than due to the experimental manipulation.

💡Fatigue Effects

Fatigue effects describe the decline in performance that can occur when participants are subjected to a lengthy or demanding experiment. The video mentions fatigue effects as a potential problem in within-subjects designs, where participants might become tired and perform worse as the experiment progresses, thus affecting the validity of the results.

💡Carryover Effects

Carryover effects occur when the effects of one treatment condition carry over into subsequent conditions, influencing the participant's responses. The video uses the example of reading books and then taking tests to illustrate carryover effects, where the knowledge gained from the first book might affect performance on the second test, making it difficult to isolate the effects of each book.

💡Mortality

In the context of the video, 'mortality' refers to the loss of participants over the course of a study, which can affect the validity of the results. This is particularly relevant in within-subjects designs where the same participants are tested multiple times, and some may drop out before the study is completed. The video points out that those who remain might not be representative of the original sample, thus introducing bias into the results.

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