Unit 2 Understanding the Individual

Methodology

You need to

Be able to describe and evaluate PET and MRI scanning techniques

Be able to describe and evaluate twin and adoption studies as research methods

Be able to describe and evaluate the use of animals in laboratory experiments including ethical and practical issues.

This lesson will be about

Twin and Adoption studies

Another method used by psychologists to tease out the effects

of Nature and Nurture

Twin Studies, adoption studiesand correlational

analysiscontribute to our understanding

of the learnt/innate debate

BackgroundHopefully you will have already read the first part of the ‘Brain’ text book (p227-239)

Ideally you will already be aware of how twin and adoption studies are used as research methods.

Remember you can be asked about ‘Underlying Assumptions’

Identify at least 2 assumptions of the following approaches in psychology:(meaning what is considered to be important within each particular approach)• Cognitive• Social• Psychodynamic• Biological

So, can you now identify 2 assumptions of the biological approach?

Nature

The ‘nature’ view of psychology suggests that all behaviour is determined by hereditary factors.

Genes are thought to provide the blueprint for all behaviours; some of these will be present at birth, and others are thought to be on a ‘pre-programmed’ schedule and will emerge as the individual matures.

NurtureThe nurture debate proposes that all human behaviour is the result of interactions with the environment.

In this debate the individual is regarded as being born with no predispositions to behaviour and so everything they do is from environmental interactions.

They are born like a Blank Slate

Watch the separated twins clipIdentify which characteristics are inherited – i.e Nature

Identify which characteristics are the product of upbringing – i.e. Nurture

http://www.youtube.com/watch?v=REhKa3_oHL8

Recap - CorrelationCorrelations show relationships between 2 sets of

data. (i.e. how closely they match)A correlation coefficient is a number between +1 and -1 expressed as a decimal . Eg +0.86The direction of the number ie positive or negative

indicates whether the relationship is positive (as one goes up the other goes up) or negative (as one goes up the other goes down)

The nearer to plus or minus one the number is shows how strong the relationship is.

When looking at twin or adoption studies we tend to look for positive relationships as it would be very strange if the closer the biological relationship the more unlike someone we were

ComparingWhen we say we compare twins, or comparing children with parents we mean on a measurable variable and because we are psychologists this will be something to do with behaviour for example

Intelligence Aggression Introversion/extroversion Sense of humour Mental illnesses such as depression or schizophrenia Psychologists talk about concordance rates

Concordance rates

Simply the correlation coefficient converted from a decimal to a percentage.

A correlation coefficient of 0.79 becomesA concordance rate of 79%

Identical twins share 100% of their DNA

Non-identical twins share only 50% of their DNA

Bouchard IQ concordance rates

Dizygotic (2 eggs) MonozygoticDZ MZ55% concordance 86% concordance

MZ reared apart 76% concordance

What does this tell us about IQ?Identical Twins

Twin studiesWith twin studies there are 2 main methods

1.comparing concordance rates of monozygotic twins with dizygotic twins

2.Comparing monozygotic twins reared together with monozygotic twins reared apart

Adoption studies

With adoption studies we tend to compare the adopted child with the biological mother and the adoptive mother to see which correlation coefficient is highest

e.g.Child and adoptive mother 0.42Child and biological mother 0.72

Siblings Sometimes but less often

sibling studies will be done where the child is compared to biological and adoptive siblings

Problems In general the problem is that there are so many variables that

come into play when comparing families.

This is especially the case when it comes to adoption and reared apart twin studies.

This enables some level of choice in families chosen by researchers which may create a bias towards what the scientist is trying to show.

i.e. support the learnt or innate debate. Scientists are not meant to favour one outcome when doing research but in this hotly debated topic they often do.

Twin and adoption studieschecking learning…

1) What are twin studies?2) Explain what is meant by concordance rates.3) Define MZ and DZ twins.4) What is meant by the terms nature and nurture?5) What are adoption studies?6) What are the problems with using twin and adoptive

studies?7) List three further issues with twin and adoption studies.

Practice

For each of the studies describe how you would use a twin study a study of twins reared apart an adoption study 1. To find out if depression is inherited.2. To investigate the nature-nurture issue.3. To find out if IQ is inherited.

Answers

To look at whether depression is inherited.Find mothers diagnosed as suffering from depression and whose children have been adopted. Find the children. Check the children for signs of depression. Check the adoptive mothers for depression. If the adopted children with depressed biological mothers have depression, it +is evidence for some genetic factor causing depression, this true if the adoptive mothers do not suffer from depression.

So for example…

To look at the nature-nurture issueFind twins that were reared apart throughout

their childhood. Check how similar the are, particularly if they have not yet met one another. Alternatively, check how similar they were when they first met as adults. If they are similar as adults, similarity is likely to be genetic.

For example….

To look at IQ and how far it might be inherited. Find MZ and DZ twins. Give both an IQ test. See

how different the scores are between the two twins. If the scores for the MZ twins are more similar than the scores for the DZ twins, then this indicates at least some genetic cause for IQ.

Gottesman & Shields (1966)

This research used twin studies to investigate whether schizophrenia has a genetic basis

It is described in your Brain text book p288

• http://www.phgfoundation.org/tutorials/twinAdoption/7.html