Types of Experiment November 17 th 2009

Experimental and Non-experimental techniques BATs Be able to describe the different types of experimental techniques in Psychological research. Identify different techniques in research studies learned so far Evaluate the strengths and weaknesses of each type of experiment Homework - Research Methods exam question sheet

Types of Research Methods Experiments- (laboratory, field and natural) Investigations using correlational analysis. Naturalistic observations Questionnaires Interviews Case Studies Content analysis Today we are focusing on Experimental methods and design

Types of Experiment You will need to know: how and when each type of experiment is used. the strengths and weaknesses of each type of experiment. The ethical issues raised when each type of experiment is carried out.

Types of Experiment Laboratory experiments Field Experiments Natural Experiments

Laboratory Experiments Conducted in a special environment where variables can be carefully controlled. Participants are aware that they are taking part in an experiment. They may or may not know the true aims of the experiment. (Is this ethical?)

Can you think of any Lab experiments covered so far? E.g Peterson and Peterson (1959) – Trigrams If you find it useful use the worksheet to summarise the different types of experiment

Strengths and weaknesses of Lab Experiments Well controlled. Permits us to study cause and effect. Confounding variables minimised. Can be replicated (copied/repeated)  Artificial or contrived.  Participants know they are being studied, which is likely to affect their behaviour.  Investigator may influence results.  The setting is not like real life – low in mundane realism.  Because IV and DV have been operationalised it doesn’t represent real-life experiences e.g. trigrams to test memory  Low ecological validity Ethical Issues Deception Informed consent (is it truly voluntary?) Psychological harm

Field Experiments Conducted in a more natural environment, i.e ‘in the field’. The Independent variable (IV) is still deliberately manipulated by the researcher. Participants are often not aware that they are participating in an experiment. Not all field studies are experiments.

Examples of Field experiments Bickman’s Study of Obedience (1974) The effects of appearance on behaviour Bickman found that New York pedestrians were more likely to obey someone dressed as a guard than someone in a milkman uniform or casually dressed. The confederates issued orders to passers-by to ‘pick up this bag for me’, or ‘this fellow is overparked at the meter but doesn’t have any change: give him a dime.’ The researcher observed and recorded their responses. Godden and Baddeley – Divers word recall expt

Strengths and weaknesses of Field Experiments Permits us to study cause and effect. Less artificial so have higher ecological validity, (Easier to generalise from results.) Avoids some participant effects (when they are unaware of study)  Less control of extraneous variables.  More time consuming, so more expensive. Ethical Issues Informed consent Difficulty debriefing Privacy

Natural Experiments The IV has not been deliberately manipulated by the experimenter, so the situation is described as ‘natural’. This method used when there are IV’s that cannot be manipulated directly for ethical or practical reasons. Not true experiments – quasi experiments, because IV not changed deliberately to see effect on DV.

Examples of Natural experiments Can you think of any we have covered so far? Bahrick et al (1975) – year book study. Hodges and Tizard study of institutionalisation.(p81) St Helena – Charlton et al (2000) – Does the introduction of TV produce an increase in anti-social behaviour? - They found that there was no change in anti-social behaviour, in contrast to a study done in Canada in1885 Williams). Reasons possibly because St Helena has a strong sense of identity and no reason to be aggressive (confounding variable?)

Strengths and weaknesses of Natural Experiments Allows research where IV cannot be manipulated for ethical or practical reasons e.g. deprivation studies Enables psychologists to study ‘real’ problems e.g the effects of disaster on health – (increased mundane realism and ecological validity) Less chance of demand characteristics or experimenter bias interfering.  Cannot demonstrate causal relationships because IV not directly manipulated.  Many confounding variables (e.g allocation of participation to groups), threat to internal validity.  Can only be used where conditions vary naturally.  Participants may be aware of being studied. Ethical Issues Informed consent Confidentiality

Which of these are lab and which field experiments? A. Helping behaviour was investigated in a study in New York subway. A confederate collapsed on a subway train and investigators noted whether help was offered. The confederate was either holding a black cane or a paper bag with a bottle of booze and smelled of alcohol (Thus appearing drunk). Piliavin et al (1969) found that when the victim carried a cane, 95% bystanders helped within 10 seconds, when ‘drunk’, help came in only 50% of trials. c. The Hawthorne Electric factory in Chicago asked researchers to study what factors led to increased worker productivity. The study found that increased lighting led to increased productivity – but then also found that decreased lighting led to increase productivity (Roethlisberger and Dickson, 1939). The conclusion was that the participants knew they were being studied and this interest in their work was what explained the increased output, masking the real IV. This is called the Hawthorne Effect B. Participants were asked to wait in a room before the experiment began. There was a radio playing either good or bad news and a stranger was present. When they were asked to rate the stranger, the degree of liking was related to the kind of news they had been listening to, showing that people are attracted to others who are associated with positive experiences (Veitch and Griffitt, 1976). A = field B = Lab C = natural

Try a field experiment! At break go out into the playground. One of you is a confederate and asks students to pick up a piece of litter. Your partner records how many people obeyed Would it make a difference if you were wearing a prefects jumper and badge or were a teacher?

It is important to choose the correct sample from your target population, this can minimise your extraneous variables. Sampling Techniques Random sampling: Everyone in the entire target population has an equal chance of being selected. Opportunity sampling: Uses people from target population available at the time. Systematic sampling: Chooses subjects in a systematic way. For example, every 10th person from a list or register. Self-selected sample: Participants volunteer. For example, by answering an advert. Stratified sampling: Divides target population into groups, people in sample from each group in same proportions as population. So you would have a higher number of people between the ages of than Do worksheet

Experimental Design In an experiment we manipulate an IV There are usually two values of the IV e.g. Noise or no noise Rhymes or synonyms These determine the conditions of the experiment The conditions can be arranged in several different ways psychlotron.org.uk

Experimental Design Independent measures Repeated measures Matched participants psychlotron.org.uk

Independent Measures Recruit a group of participants Divide them into two This group does the experimental task with the IV set for condition 1 This group does the experimental task with the IV set for condition 2 Measure the DV for each group Compare the results for the two groups psychlotron.org.uk

Repeated Measures Recruit a group of participants Condition 1Condition 2 The group does the experimental task with the IV set for condition 1 The group repeats the experimental task with the IV set for condition 2 Compare the results for the two conditions psychlotron.org.uk

Matched Participants Recruit a group of participants Find out what sorts of people you have in the group Recruit another group that matches them one for one Condition 1Condition 2 Compare the results for the matched pairs Treat the experiment as independent measures psychlotron.org.uk

Participant Variables Variation between PPs can affect DV Could mask an effect (false negative) Could imply an effect where none exists (false positive) This is a problem with independent measures Control by random assignment to groups Use repeated measures or matched PPs instead psychlotron.org.uk

Fatigue, Boredom & Practice (fatigue and practice effect) Carrying out a task repeatedly leads to changes in performance Deterioration as PPs become tired or bored Improvement due to practice This is a problem with repeated measures Leave a long gap between conditions Counterbalanced design (e.g ABBA) Use independent measures or matched participants psychlotron.org.uk Jot down an example of counterbalancing – p77 of text

Over 2 U!! You are now going to plan and carry out your first Psychological experiment!! Ethical considerations Ask permission to use people as participants, get their informed consent Debrief them after as a way of preventing deception. Respect their privacy and names should not be reported to allow for confidentiality I would like you to replicate Miles and Hardman’s 1998 experiment mentioned on p26 of Exploring Psychology.

Over 2 U!! An alternative experiment can be found on p77 ‘over to you’. You will plan it today and carry out the experiment next week period 1 with Year 8 as your participants! Today you will need to prepare any wordlists, consent forms, debrief slips, data collection tables, standardised instructions e.t.c Next week we will collect and analyse data Be prepared to present findings next week to rest of class!!!! GOOD LUCK!!! Use the Project brief sheet to help you

Homework Research Methods exam question sheet In next week please