Methods to Control Extraneous VariablesContent Covered-Placebo effects-Experimenter effects-Experiment designs-Statistics-Inferential statistics-Ethical considerations in psychological research

Study Design Contentorder effects, experimenter effect, placebo effects;

ways of minimising confounding and extraneous variables including type of experiment, counterbalancing, single and double blind procedures, placebos; evaluation of different types of experimental research designs including independent-groups, matched-participants, repeated-measures; reporting conventions

statistics: measures of central tendency including mean, median and mode; interpretation of p-values and conclusions; reliability including internal consistency; validity including construct and external; evaluation of research in terms of generalising the findings to the population

Study Design Content• ethical principles and professional

conduct: the role of the experimenter; protection and security of participants’ rights; confidentiality; voluntary participation; withdrawal rights; informed consent procedures; use of deception in research; debriefing; use of animals in research; role of ethics committees.

Placebo Effects In psychological research a placebo effect may occur

when a participants response (the DV) is influenced not be the IV, but rather than by the expectancy of the participant of how they are expected to behave

For example… If a study was examining a new drug and we had an

experimental group who was receiving the drug in a tablet and a control group who was not, the participants who know they are receiving the treatment may have effects based upon their expectancy of what they think should happen

Box 6 – The Hawthorne Effect, pg. 21

Placebo EffectsTo counter this the experimenter may

use a placebo

A placebo is a fake treatment which is used to reduce participant expectancy in a treatment. It could be in the form of a sugar pill so that both the experimental and control groups are unsure as to what group they are in

This is known as a single-blind procedure

Experimenter EffectsEven though we may have

minimised participant effects via single-blind procedure, there still could exist experimenter bias

Experimenter bias is where the experimenter may have expectancy about the results based upon the treatment

Experimenter EffectsTo overcome this extraneous variable, a

double-blind procedure may be used

A double blind procedure is where neither the participants nor the researcher conducting the experiment, knows which participants are in experimental or control group

A third person is used to oversee the placement of the participants into the groups

Learning Activity 7 – Review Questions, pg. 23

Experimental DesignThe experimental design is another

way to minimise the effects of extraneous variables

There are three main experimental designs we can use in psychological research

They are Repeated measures, Matched participants and Independent Groups

Repeated-MeasuresIn a repeated-

measures design, one group of participants undertakes both experimental conditions (the experimental condition and the control condition)

Fig 1.18 pg. 28

Repeated-MeasuresAdvantages

Subject variables are kept highly controlled as they are consistent between conditions

Fewer participants are required

Disadvantages

Repetition effects may occur – participants may become bored or fatigued after the first condition

The practice effect could make the results invalid – participants may learn how to improve in the second condition from the first condition they undertake

CounterbalancingTo overcome the effects of

repetition, the experimenter may use counterbalancing

Counterbalancing involves placing half the participants in the experimental group and half in the control group first, thereby balancing the effects of the order

Matched-ParticipantsA matched-participants

design involves placing equivalent pairs of participants into each group

Participants in each condition are paired according to any important variables, which if left uncontrolled, may confound the results – could include gender, age, intelligence

Fig 1.19 pg. 29

Matched-Participants Advantages

Eliminates order effects such as fatigue as the participants only undertake one condition

Disadvantages

Although it attempts to keep subject characteristics constant, participants can never be perfectly matched

The process of matching participants is time-consuming

If one participant leaves the experiment the matched participant in the other group must have their results exluded

Independent-Groups DesignThe independent-

groups design using random allocation to assign participants to one of the control or experimental group

Each participant only undertakes the condition they are assigned to – either the control or experimental group Fig 1.20 pg. 30

Independent-Groups DesignAdvantages

Easier to select participants

Also eliminates order effects such as fatigue

Disadvantages

Subject variables could occur despite random allocation

Participants only undertake one condition

The least effective in minimising extraneous variables

Experimental DesignCopy Figures 1.18, 1.19, and 1.20

into your notes

Activity 9 – Research Methods, Minimising extraneous variables

StatisticsQuantitative statistics take the

form of numerical values such as the weight of a participant

Qualitative statistics are factual descriptions about the characteristics of a subjects behaviour and is usually in the form of words

StatisticsThere are three measures of

central tendency◦The mean – the average of a set of

scores, the most sensitive measure of central tendency but can be distorted by extreme high or low values

◦The median – the middle number in a set of scores

◦The mode – the most commonly occurring number

Inferential StatisticsInferential statistics are formal data analyses

that measure the likelihood of results obtained for a study occurring by chance

Measures of statistical significance indicate whether or not the results obtained in an experiment are due to chance, rather than the manipulation of the IV

Significance refers to the results being important, if the results are significant then they important in terms of supporting the hypothesis

p-valueThe p-value is an inferential

statistic used to represent the probability level for deciding whether chance factors are responsible for the results obtained

If the results are obtained by chance then our hypothesis cannot be supported

p-valueA significant result is where it has been determined

there is a low probability that the results of a research study were due to chance

A p-value of p<0.05 occurs when there is probability of chance occurring 5 or fewer times in 100 repetitions of the research

In psychology a p<0.05 is accepted to mean that the results are statistically significant and are not due to chance, but rather due to the influence of the IV

We can also say that the hypothesis is supported if p<0.05

p-valuep-values with stricter conditions are also

used when the researcher wants to be really sure of their results (a final drug trial before human subjects are used perhaps?)

For example p<0.01(chance less than 1 in 100) or p<0.001(chance less than 1 in 1000)

Learning Activity 15 – Review Questions

Conclusions and GeneralisationsA conclusion is a decision or

judgement made about the results from an investigation may mean

A generalisation is a decision or judgement made about how the results could be applied to other members of the population which is being studied

Ethical Considerations in Psychological Research

The term ethics refers to standards that guide individuals to acceptable or desirable conduct

Ethics are present in many different fields and organisations (Schools, law etc.)

The “National Statement on Ethical Conduct in Research involving Humans” is a code of ethics which provides guidelines which must be followed when working with people in research situations and all other areas of professional practice

Participants’ RightsConfidentiality

Voluntary Participation

Informed Consent Procedures

Withdrawal Rights

Deception in Research

Debriefing

ConfidentialityRefers to a participants right to

privacy, so that details of their involvement in the study cannot be revealed in a manner which enables individuals to be identified, unless written consent in obtained

This can refer to access of data from the research as well as storage and disposal of research data

Voluntary ParticipationThe researcher must ensure that

a participants participation in a research study is entirely voluntary and that no pressure is placed on them to take part

Informed Consent ProceduresWhere possible participants must

be informed of the nature and purpose of the research

This informed consent needs to be documented and is usually done in the form of a consent form

Informed Consent ProceduresWhere research may involve participants in

situations of physical or mental stress, the researcher must inform them of the procedures to be used and the effects that can be expected

If research involves participants in high levels of emotional arousal, the researcher must ensure no psychologically vulnerable person participates

Where an individual is unable to give informed consent (such as a child or intellectually disabled individual) the researcher must obtain appropriate consent from those legally responsible for the individual

Withdrawal RightsThe researcher must inform the

participant that they are free to participate or decline to participate or withdraw at any time

The participant must be free to withdraw from the research at any time, without giving a reason

Deception in ResearchSometimes, giving a participant too

much information about a study may influence their behaviour during the study, therefore influencing the results

When it is necessary to conduct a study without fully informing the participants of its true purpose prior to the study, the researcher must ensure that participants do not suffer distress and are fully debriefed at the end of the study

DebriefingIt is important that the

researcher debriefs the participant in regards to the research and results following the conclusion of the research

Learning Activity 19 – Identifying ethical issues, pg.54