How does a psychologist design an investigation?
The starting point forany research studyis to generate appropriate aims. Aims are general
statements ofwhat the studyis tryingto do and whyit is being carried out.Forexample, the aim is
to investigate whethergiving children vitamin pills improves their IQ.
The aim ofteninvolves testing one ormore hypotheses. A hypothesis is a clear, testable statement.
It is a prediction made at the beginningof the study,written in the present tense. For example,
participants wholearn a wordlist before sleeping recall more wordsthan those wholearn the list
after waking. There are two kinds ofhypothesis:
1. A directionalhypothesispredictsthe direction in whichresults are expected to occur.For
example, more wordsare recalled correctlyfrom a list whenusingrehearsal as a memory
improvement technique thanwhen nomemory improvement techniqueis used. Inthis
case, weare predictingnot only that there will be a difference between the numberof
wordsrecalled, butthat more will be recalled in one conditionover another.
2. A non-directionalhypothesisdoesnot predict the expected directionof the difference.For
example, there is a difference inthe number ofwordscorrectly recalled from a list when
presented with backgroundmusic thanwhen nomusic is presented. This hypothesis still
makes a prediction,but doesn’t state whichconditionwill lead to better recall.
Psychologyteachers preferthe taste of Coca-Colatothe taste of Pepsi.
The consumptionof daily fishoil supplementswill have aneffectonthe
concentrationlevelsof childrenwhencompleting schoolwork.
There will be adifference betweenthe numberof attemptsneededtolearn a
simple maze bya groupof five ratsand byOne Direction.
Womenare more likely thanmentowaitfora greenlighttoappearat a
pedestrian crossingbefore crossing.
There will be adifference betweenthe scoresof malesandfemalesona
There will be adifference betweenthe numberof tomatoesproducedby
plantsingrow bagsand plantsinthe ground.
Bullswill charge more oftenwhenpresentedwitharedrag, than when
Childrenaged5-10 are able toname more cartooncharacters than teenagers
A variable is just something that can change, or vary. In an experiment theresearcher is
trying to find out whether a particularvariable, the independent variable (IV) has an effect
on a specific aspect of human behaviouror mental process, thedependant variable (DV).
However, in order to be certain that any changes in the behaviourbeing measured are
caused by themanipulationof theindependent variable,everything else must becontrolled
bythe researcher and kept constant. For example, in an experiment investigating the effect
of noise (IV) on memory (DV)all othervariables, called extraneous variables, must be
controlled,such as thetime given to each participant to learn thematerial to be
memorised, thetesting room, temperature and thetime of daythe testing takes place.If
these extraneous variables are not controlled thentheycan confound thefindings of a
study, and so become confoundingvariables.
The variables in an experiment are referred to as theIV and theDV. However, in a
correlational investigationtheyare referred to as co-variables since theaim is to discover
whethertwo variables are related to each other,not whetherone (IV) directly affects
Research Study Extraneous Variable(s) How could it be overcome?
An investigationinto the effect of
organisationon memory. A list of 50
items that couldbe bought at a
supermarket were used. One group
saw thewords organised into
categoriessuch as fruit, dairyproducts
and cleaning materials. The other
group saw the same words presented
An investigationinto the effects of day
care on aggression. A group ofchildren
who started daycare before theageof
two years were compared with a group
of childrenwho started after theageof
two years. The researcher assessed
each childandgave them an
An investigationinto the effect of
rewards in highereducation.One
collegeoffered a £20.00 reward to its
students for each AS level they
achieved at gradeA. A different college
in the same area didn’t giveany
monetary awards to its students for
achieving an A grade.
The term operationalisationmeans defining all variables in such a way as to beable to
measure themin a specific way. For instance, there is no single way to best measure some
psychologicalconcepts,such as aggression and memory. Therefore, psychologistsdefine
each variablein terms of theoperations takento measure it. For example, in an
investigationthat involves measuring memory, thepsychologist couldoperationalise
memory in terms of the number ofcorrectly recalled words from a list of twenty. This is a
What is an experiment?
Hypothesis Operationalisation Independent
Gender affects sports
There is a gender
difference in thenumber of
to form a mental
word or being
recalled from a
A person experiencing a sad
moodwill comfort eat
The viewing of a happy
movie will leadto less
compared to theviewing of
a sad movie.
number of real-
made up of 50
adults or no
thetime taken to
Daycare affects a child’s
A childwho starts day care
before theageof 2 years
has fewer friends thana
childwho starts daycare
after theage of 2 years.
Anexperiment involves an investigation into whether an independent variable,eithermanipulated
by the researcher or naturally occurring,hasan effecton anaspect of behaviour,termed the
dependent variable.There are numberof waysof conductingexperimentseach with their own
This takes place in a carefully controlled setting. The researcher manipulates the
independent variable, the thing that they decide to change,whilst measuring the
effectsof that changeon the dependent variable, the thingthat they measure. A
standardised procedureis used, so that eachparticipant is treated in exactly the same
way.It is important tonote that it doesn’t have to be a sciencelab, a roomset aside
fora Psychologyexperiment would still be classed as a laboratory.
This takes place in a natural setting, like a towncentre,hospital wardor a work
office.Aswith a laboratory experiment, the researcher still manipulates the
independent variable and measures the effectsof that changeon the
dependent variable. A standardised procedureis used, so that eachparticipant
is treated in exactly the same way.
A naturally occurringindependentvariable is utilised, so the researcher doesn’t manipulate it
themselves. Forexample, comparingthe effectson an infantof the length oftime spent in day care.
The researcher cannotmanipulate how long a child spendsin day care, as this is decided by
somebody else, usually the child’s parents.However, the researcher canutilise this naturally
occurringvariable and conductaninvestigation. The experiment may take place in a laboratory or a
A psychologistbrought40 professional athletes into a medical research
facility at his university and tested their physical stamina before and after
taking a courseof multivitamins and minerals.
A psychologistput upposters advertising for university studentsto take part
in a study onreaction times. They had to pressa buttonona keyboard when
an ‘x’ appeared on a screen.
A psychologistwent shoppingin Newcastle wearing a Sunderland football
shirt on matchday. He pretended to collapse on the pavement and counted
whether more Newcastle or Sunderlandsupporterscame to help him.
A psychologistvisited the toilets of his local nightcluband conductedastudy
where he invaded the personal space ofother men at the urinals and noted
how long it took forthem tostart urinating.
A psychologistconducteda studywhere he comparedthe self-perceptions of
patients sufferingfrom anorexia nervosa, bulimia nervosaand obesity.
1. As a research psychologist youhavebeen approached bythegovernment to
investigatethe aggressive tendencies of a new breed of dog,the‘Chavadidas’,to
see whetherit shouldbe placed on thegovernment’s dangerous breeds list or not.
What would theprocedure for each of thefollowing typesof experiment consist of?
Laboratory Field Natural
2. As a research psychologist youhaverecently read that taking
omegafish oilsupplements can improve your brain function, aiding
concentration, memory and possiblyeven intelligence.In
preparationfor your AS Psychologyexaminations youdecideto
undertake three experiments to investigatewhetherit is worth
taking a course of omegaoils. What would theprocedure for each
of thefollowing typesof experiment consist of?
Laboratory Field Natural
What is an experimental design?
The way in which the participantsare ‘organised’ into groups in an experiment is called the
design of theexperiment. There are 3 different experimentaldesigns used by
1. Independent groups:Thisinvolves different groups of participantsin each
conditionof theexperiment. It may consist of a control conditionandone or more
experimental conditions.For example, one group of participantstakea new anti-
depressant daily,whereas theothergroup
takeno drug. Thetwo groups are
compared after 6 weeks in terms of the
severity of theirdepressive symptoms.
2. Repeated measures:This involves the
same group ofparticipantsin each
conditionof theexperiment. For example,
theparticipantsare given a speech to learn
whilst thetelevisionplayed in the
background and were then tested on their recall. They were thengiven a different
speech to learn in a silent room and theirperformance was compared with their first
3. Matched pairs: This involves different groups of participantsin each conditionof
theexperiment. However, each participant in thefirst conditionof theexperiment is
matched closelywith anotherparticipant in thesecond conditionon all thevariables
considered to be relevant to theexperiment. For example, participantsmay be
matched for age beforean investigationinto the effect of music on memory, since
age mayconfound thefindings of thestudy.
Alton Towers have commissioned youto conduct research into whether rollercoasters or
water rides are more exciting for visitors. Howwould you carry out FIELD experiments
using each design?
Independent Groups Repeated Measures Matched Pairs
Design Advantages Disadvantages How could you deal with this
Example Which experimental
design was used?
1. In order to assess theeffects of fatigueon reactiontimes, a researcher gave
participantsa target detectiontest in which theypressed a buttonevery
time a dot appeared on a screen. The time between thedot appearing and
thebuttonbeing pressed was recorded. The participantsdidthetest twice,
once first thing in themorning and once last thing at night.
2. In order to compare theeffectiveness of two different typesof therapyfor
depression, depressed patients were assigned to receive eithercognitive
therapyor behaviourtherapyfor a 12-week period.The researchers
attempted to ensure that thepatientsin thetwo groups hada similar
severity of depressed symptoms by administering a standardised test of
depression to each participant,thenpairing them according to the severity
3. In order to assess theeffect of organisationon recall, a researcher
randomly assigned student volunteers to two conditions.In conditionone
theparticipantsattempted to recalla list of words that were organised into
meaningful categories, whereas in conditiontwo the participants
attempted to recall thesame words, randomlygrouped on thepage.
4. In order to assess thedifference in reading comprehension between 7 and
9-year-olds, a researcher recruited a group of each from a localprimary
school.Theywere given thesame passageof text to read, and then asked a
series of questions to assess their understanding.
5. In order to assess theeffectiveness of two different ways of teaching
reading, a group of 5-year-olds were recruited from a primary school.Their
level of reading abilitywas assessed, and then theywere taught using
scheme 1 for 20 weeks. At theend of thisperiod,their reading was
reassessed, and a reading improvement score was calculated.They were
then taught using scheme 2 for a further 20 weeks and anotherreading
improvement score for thisperiodwas calculated.The reading
improvement scores for each childwere thencompared.
1. Why it was necessary to use a matched pairs designin experiment 2?
2. If you were to redesign experiment 5to use a matched pairs design, what variable(s)
would youuse to match theparticipantsand why?
3. Can you suggest whya repeated measures design would beinappropriate for
4. Are thereany disadvantages of a repeated measures design that couldaffect the
findings of experiment 1?
5. How couldcounterbalancing beused in experiment 5?
6. Are thereany participant variables that couldhave affected thefindings of
7. How didtheresearcher in experiment 3 try to avoid theproblemof participant
A psychologist showed participants100 different cards, one at a time. Each card hadtwo
unrelated words printed on it, eg DOG, HAT. Participantsin one group were instructed to
form a mental image to link thewords. Participantsin theothergroup were instructed
simply to memorise thewords. After allthe word pairs hadbeen presented, each
participant was shown a card with thefirst word of each pair printed on it. Participantswere
asked to recall thesecond word. Thefollowing results were found.
a) What is theindependent variable (IV)in thisstudy? (2 marks)
b) What is thedependent variable (DV)in this study?(2 marks)
c) What experimental design was used in thisstudy? (1 mark)
d) Explain one strength of this experimentaldesign in thecontext of this study. (2
e) Explain howa psychologist couldfindout whetherthese results are reliable.(2
A researcher carried out an experiment to investigatehow many numbers couldbe heldin
short-term memory. Theparticipantswere 15 childrenand 15 adults.Participants were
asked to repeat lists ofrandom numbers, in thecorrect order, as soon as theywere read out
bythe researcher. For example, when theresearcher said, “3, 4, 2, 8” theparticipant
immediatelyrepeated “3, 4, 2, 8”. When theresearcher then said, “7, 5, 9, 6, 4” the
participant immediatelyrepeated “7,5, 9, 6, 4”. One number was added to the list each
time until participantswere unable to recallthe list correctly. Each participant’smaximum
digit span was recorded.
a) Write an appropriatenon-directional
hypothesisfor thisexperiment. (2
b) Explain whythe researcher used an
independent groupsdesign for this
experiment. (2 marks)
c) Write themode for each group in the tablebelow. (2 marks)
d) What does thefrequency distributionshowabout the results? (3 marks)
A psychologist carried out an experiment using an independent groupsdesign. The
psychologist wished to investigatetheeffectiveness of a strategyfor memory
improvement. In one condition,participantswere taught amemory improvement strategy.
In theothercondition,participantswere not taught thismemory improvement strategy.All
participantswere asked to memorise 10 pictures of familiar objects.For example, the first
was a doll,thesecond was an apple.All participantswere then given 50 pictures each, and
asked to select theoriginal10. The psychologist didapilot studybeforecarrying out the
a) Write a directionalhypothesisforthisexperiment. (2 marks)
b) Explain what is meant byan independent groups design. (1 mark)
c) Explain one strength and one limitationofusing an independent groups design. (2 +
A researcher investigated the effect of age of starting day care on levels ofaggression.
Four-year-old childrenattending a daynursery were used. Each childwas assessed by the
researcher and given an aggression score. A high score indicated a high levelof aggression.
A low score indicated alow level of aggression. The maximum score was 50.
Mean aggressionscores for four-year- old children who had started day care before the
age of two or after the age of two
a) Identifytheoperationalised independent variable and theoperationalised
dependent variable in this study. (2 + 2 marks)
Operationalised independent variable
Operationalised dependent variable
b) What do themean scores in Table 1 suggest about theeffect of ageat which
children started daycare on children’saggression? (2 marks)
c) Statean appropriatedirectionalhypothesisforthis study. (2 marks)