Research Methods example 2
I want to test the effect of Hours spent Studying on Exam Performance.
VARIABLES
The Independent Variable is Hours spent Studying (this is what I want to see the
effect of, what I am going to vary or manipulate, I am going to get people to either
study or not study and then take an exam)
The Dependent Variable is Exam Performance (this is what I am going to measure
to see any effect the IV has had, I am going to record their performance on the exam)
FINDING A SAMPLE OF PARTICIPANTS
My Population of interest is all year 12 students in Victoria. Obviously I cannot test
every year 12 student in Victoria so I will draw a smaller sample of students to
represent the larger population.
Before I draw my sample I need to consider if there are any groups within my
population of interest that may test differently to other groups. If there are I need to
make sure that these groups are represented in my sample, if they are not then my
sample is not representative and my results will be meaningless.
For example the type of school attended by the students (public or private) in my
study may affect their exam performance. Thus I need to make sure that I use
stratified sampling. I must divide the population into groups based on the type of
school attended, (eg. Public or private) and then draw my sample randomly from
within each of these groups. Doing this will ensure that my sample contains the same
proportions of males and females as appear in the population.
Eg. If in the population 50% of students attend public schools and 50% attend private
schools and I am drawing a sample of 100. To stratify my sample and make it truly
representative of the population I must randomly draw 50 public students and 50
private students from the population.
EXPERIMENTAL AND CONTROL GROUPS
To test whether studying effects exam performance I need to organize my experiment.
I need to divide my participants into two groups. One group will study and then
complete the exam; the other group will not study and then complete the same exam.
Doing this allows me to compare the performance on the exam of people who studied
Vs people who did not study.
Group One is the Experimental group – they were exposed to the IV (studying)
Group Two is called the Control group – they were not exposed to the IV (they did
not study)
Now I can compare the difference in performance between the experimental and
control groups and find out if studying affected exam performance.
Wrong answer dumb arse!!!
If you study you will do well you
stupid little boy!!!
EXTRANEOUS VARIABLES
Once I have obtained my sample of students I must consider other factors before I
assign participants to the experimental and control groups. There are lots of things
which are specific to the individuals I have chosen for my study that may affect exam
performance other than studying. These factors are called extraneous (uncontrolled)
variables
These might include: intelligence, anxiety, previous experience etc.
If I simply use random allocation to decide who will be in the Experimental and
Control groups I may get a severe mismatch that will affect my results. For example
my experimental group may have all of the students who are intelligent and my
control group may have all of the students who are not intelligent!
Eg. If by chance my experimental group contains all of the students in my sample who
are intelligent then I cannot know if my experimental group performed better on the
exam because they studied or because they were just smarter than the control group!
Now my results are meaningless! I don’t know if it was studying or intelligence that
effected exam performance.
If this happens the extraneous variable has become what we call a confounding
variable. We don’t know which variable has had an effect, our IV or the extraneous
(now referred to as confounding) variable.
Was it studying?
OR
Intelligence?
that caused our experimental group to perform better?
CONTROLING EXTRANEOUS VARIABLES
To control extraneous variables we need to make our experimental and control groups
as similar as possible. If they are identical in almost every way then any difference
between them should be due to the effects of the IV not other factors.
Eg. If we make sure that there is the same number of intelligent and stupid individuals
in the experimental and control groups then intelligence should not create a
difference in exam performance between our groups. Any difference in exam
performance should be due to the effects of studying.
There are a number of ways we can ensure our experimental and control groups are as
similar as possible on all factors except the IV
Repeated Measures Design (Stroop used this)
Each participant is involved in both the experimental and control conditions. This
design controls or eliminates any effects that might be attributed to participant's
personal characteristics, since they remain constant. Also known as the within
participants design.
Little Jimmy will first complete the
Little Jimmy will then complete an
exam without studying
equivalent exam after studying
CONTROL GROUP
EXPERIMENTAL GROUP
Note that an equivalent
exam is used in the
second condition.
Why am I in your study
again Mr Brinkman???
Quiet Jimmy!!!!!
The only problem with this is that participants’ performance on the second condition
may be affected by their past experience of having done an exam before. This is
called Order Effect. Counterbalancing is used to control this. Counterbalancing
involves making half of the participants do the two conditions in one order (control
then experiment) and the other half in the opposite order (experiment then control)
Matched Participants Design – Paired up
Involves selecting pairs of participants who are similar in characteristics that can
influence the dependent variable, on the basis of scores achieved on a pre-test, or a
number of pre-tests. Participants are then ranked and paired in accordance with their
scores and then one of each pair is allocated to the experimental and the other to the
control group. Doing this ensures the experimental and control groups are as similar
as possible on all other factors other than the presence of the Independent Variable
All participants are given an intelligence test prior to our study beginning. The two
participants with the worst IQ are paired up. One of the pair is then assigned to the
experimental group the other to the control group.
Eg. Fred and Johnny were the two participants who scored lowest on the IQ test
Fred scored equally as bad as Johnny on
the IQ test. Fred is now assigned to the
CONTROL GROUP
Johnny scored equally as bad as Fred
on the IQ test. Johnny is now assigned
to the EXPERIMENTAL GROUP
I may look
cool but
I’m really
stupid!
Duh!
Independent Groups Design
Allocates participants to groups via a random procedure such as the toss of a coin.
Then all those who toss a head might be allocated to the control group and all those
who toss a tail to the experimental group. This only works when our experimental and
control groups are very large. The idea being that if we have enough people then most
of the extraneous variables will cancel themselves out just by chance!
Boris tossed a head so he goes into the
CONTROL GROUP
Some dude in a suit of armour tossed a tail
so he goes into the EXPERIMENTAL
GROUP