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16 | A2 PSYCHOLOGY: THE STUDENT’S TEXTBOOKa notice board or newspaper advertisement may beused to ask for volunteers to respond.Generalisability and biasThe findings of the research may lack generalisabilitybecause a volunteer sample may consistof mostly helpful, interested, more motivated orobedient people and as such it may not be like thegeneral population. In addition to this a volunteersample may be open to bias as those who take partmay do so in order to seem helpful and so pleasethe researcher – who is often their psychology lecturer,and who therefore has the power to providegood marks on their work!Issues of reliabilityReliability refers to how well the research can bereplicated at another time, or if two researcherscarried out observations how well their opinions ofwhat was observed agree. In short, reliability refersto the consistency of the research. As reliabilityincreases so does our confidence in the results.Observer reliabilityA widely used method and technique in psychologicalresearch is observation. Here the researchersobserve behaviour, marking down what theysee. Often they are looking for particular types orcategories of behaviour. For example, researchersmay be interested in investigating whether malechildren behave more aggressively at play whensurrounded by other males or when in a mixedmale/female environment. In this case researcherswould observe the behaviour of males in a maleonlyplay environment, recording the number oftimes they saw aggressive behaviour. They wouldthen compare these results with similar observationsmade in a mixed male/female environment.The results of research like this will not be ofmuch use if the observations are not done in thesame way – i.e. if they are not consistent. Weneed to ensure that another person observingthe behaviour would come up with the same, orat least a very similar, result. For this reason twoobservers make observations at each session. Theirresults are compared for similarity. If the two setsof observations are similar then we can say thatthere is good observer reliability.Assessing observer reliabilityComparing the observations of two observers isbest done using correlation. This relatively simplestatistical technique allows us to see how similartwo sets of values are. A good positive correlationshows that the two observers provided similarresults. If you can show a good positive correlationto two observations of the same event then youcan say confidently that you had good observerreliability.Improving observer reliability1. TrainingIf the two observers are able to easily identify thetype of behaviours they are watching then theywill be able to record those behaviours efficiently.Practice certainly makes perfect as observation is agreat skill. Until you try it, you’ll not fully believehow fast the different behaviours come and howvaried the behaviours that might be recorded arein different situations. For this reason, carefullytraining the observers before the research beginsis advisable as a means of improving observerreliability.2. OperationalisationBoth observers have to be clear exactly what theyare looking for. For instance, if they are observing‘helping’ behaviours then they must agree whatthis means. For instance, how ‘helpful’ does abehaviour need to be before they record it as‘helpful’? If the definitions of the behaviours tobe observed are clear and carefully laid out thenobserver reliability will be better than if categoriesof behaviour are badly defined.3. View of the behavioursEach observer must have the same ability to seethe behaviours being observed. The best way todo this is to have them both base their recordingsof behaviour on exactly the same video filmof the behaviours being recorded. This ensuresthat each observer sees exactly the same things.If the observations are recorded ‘live’, perhaps bywatching behaviours in a school playground, thendifferent sight lines may mean that incidences ofa behaviour may be missed by one observer butrecorded by the other. This would weaken thecorrelation between their results, and so weakenobserver reliability.Test reliabilityVarious tests are employed in psychologicalresearch to measure behaviour. If a researcher isinterested in assessing someone’s personality thenthey can use a test carefully designed to do thejob. These tests are often in the form of questionnairesand measurement scales that require theparticipants to indicate opinions of things, andhow they might respond or behave in differentsituations.Extract from A2 Psychology: The Student’s Textbook © Nigel Holt and Rob Lewis ISBN: 9781845901004 www.crownhouse.co.uk
DESIGNING PSYCHOLOGICAL INVESTIGATIONS | 17Assessing test reliabilityAssessing test reliability is very similar to assessingobserver reliability. The method used here istest–retest assessment, or test–retest correlation. Herethe test is given to the person again, on a differentoccasion. The person’s responses to the test oneach occasion are compared and a correlationcarried out. If there is a high correlation betweenthe responses on each presentation of the test thenwe can say that there is a high level of test–retestreliability. This means that the test measures whatit says it does consistently.Improving test reliabilityAltering the test to improve correlationIf the test–retest correlation is low, then the reliabilityof the test is in question. This means thatthe researchers must alter the test to improve thisreliability. They can do this by looking carefully atthe test itself, and identifying the parts of it thatdid not correlate well on the two occasions it wasgiven. They can then remove those componentsof the test that are weakening its reliability andreplace them with alternative questions and tasks.This new test is then tested again, to see whetherreliability has improved, using the test–retest correlationassessment. This process is repeated untila high level of test–retest reliability is shown by astrongly correlated first and second running of thetest.Assessing and improvingvalidityValidity refers to how well the test or researchactually measures what it says it measures. A tapemeasure, for instance, is a very valid tool for measuringheight, but a stop-watch is not. Similarly,research that aims to measure the relationshipbetween mathematics ability and age is valid if itdoes just that, but not if it actually measures therelationship between age and general intelligence.Internal validityInternal validity is the extent to which we can saythat our findings are truly to do with what wethink they are to do with, rather than somethingthat we have no control over. For instance, we maybe interested in investigating whether memoryability is improved by eating chocolate. We mustbe sure that the person has not secretly drunklots of cups of tea before the experiment. If theresults of our research showed that their memorywas indeed improved by chocolate eating we cannotbe absolutely sure that the tea did not havesomething to do with it, and so the task has lowinternal validity.Improving internal validityAnything that influences the dependent variable(in this case the score on a memory task)rather than our independent variable (here it’schocolate eating) reduces the internal validity ofour research. In general these things are describedas extraneous variables. If an extraneous variable(such as fatigue or practice) influences our findings,then internal validity is reduced. One of themost important aspects of research design is tominimise the influences of extraneous variables.Improved internal validity comes from improvedresistance of your research to the influence ofextraneous variables. This is best achieved by verycareful research design and planning.External validityThe results of our research have external validityif they can be generalised from our sample to thegeneral population, in other settings beyond thosein which the research was carried out and at differenttimes.Ecological validityThis is a form of external validity. If the researchhas high ecological validity then we can say thatthe results relate to different situations from thosein which the research was carried out. Some workcarried out in a laboratory, for instance, may lackecological validity, because outside the carefullycontrolled environment of the laboratory peoplemay behave differently.Just because something is done in a labdoes not mean that it lacks ecologicalvalidity. Findings from laboratory basedresearch may transfer to other settingsvery well. Be careful of this in the exam.Don’t just say ‘It lacks ecological validity becauseit was done in a lab’. This won’t get you marks. Bemore specific. Explain what circumstances outsidethe lab might bring the ecological validity intoquestion.Population validityIf research has high population validity then thefindings can be said to relate to the general population.For instance, if a piece of research has usedan opportunity sample of 10,000 people chosenfrom 20 countries worldwide, its findings are morelikely to be relevant to the whole population of theExtract from A2 Psychology: The Student’s Textbook © Nigel Holt and Rob Lewis ISBN: 9781845901004 www.crownhouse.co.uk
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