A2 Science In Society 3.3 Teacher Notes

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Copies may be made for UK in schools and colleges

A2 Science In Society 3.3 Teacher Notes

Introduction

Note that this activity, while being in the style of the Unit 3 exam, has not been subject to the careful evaluation and revision of questions undertaken by AQA during the preparation of operational exam papers.

Suggested answers

(a) (i) This is an example of evidence often used in arguments to support explanation A:

“There has been a ten-fold increase in autism and related forms of brain damage in the last 15 years, roughly coinciding with MMR’s introduction.”

Explain what is wrong with an argument to support explanation A based on this evidence.

correlation does not equal causation

many other environmental changes in last 15 years

no causative mechanism

does not provide evidence against B

(2 marks) (HSW Bc Bj)

(ii) Suggest one other environmental factor that might affect brain development in some way.

family stress/poor parenting

malnutrition in womb

use of drugs

(1 mark) (SE Jj, Jk)

(b) DSM is the manual, used by most doctors, that gives criteria used to diagnose many mental illnesses, including autism. In 1994 DSM-IV replaced DSM-III. DSM-IV changed the criteria for autism to include the milder ASD. Suggest some reasons why diagnostic criteria change over time in this way.

more research/better understanding of the problem

more experience of diagnosis by doctors/ clearer diagnostic guidelines, such as DSM

social pressure from parents/autism more acceptable than retardation

no diagnosis of a mental condition is precise/ individuals all show different symptoms

trend in successive DSM has been inclusion of more symptoms as indicative of increased diagnosis

(2 marks) (Ea, Ef, Fa, Fb)

(c) In order to test explanation B researchers re-interviewed and re-tested 20 adults who had been diagnosed with mental retardation and developmental language disorder as children.

The researchers found that at least 34% of these would now be diagnosed as having autism spectrum disorder, ASD.

Explain how this finding could be used to support explanation B.

ASD has broader criteria than autism

If other diseases now redefined as ASD

more cases of ASD would be found

although no real change in number of people with a developmental disorder

(2 marks)

(d) One attempt to improve diagnosis of autism is by the use of MRI scans of the brain. Researchers found that the brains of those with ASD had some characteristic features in parts of the cortex, such as differences in thickness or folding, compared with controls. They taught a computer to classify brain scans according to five of these features, using 20 ASD subjects and 20 controls.

Figure 2 shows how the computer performed in diagnosing ASD on the basis of the 5 features B, C, D, E and F.

Figure 2., Graphs for the five discrete features, in the left hemisphere (X), and in the right hemisphere (Y). Individual points on the graph depict classifications on the basis of different features B -F represent other features.

(i) What is the false positive rate for feature F in the left hemisphere?

0.2

(1 mark) (HSW Aa)

(ii) Considering the five features B – F in both the left and right hemispheres, which one would provide the most reliable indicator of an ASD diagnosis? Justify your answer.

left

B

highest true positive

lowest false positive

(3 marks)

(iii) Using only indicator B in the left hemisphere to diagnose ASD in a sample of 100 people without ASD how many would be incorrectly identified as being affected by ASD? (False positives)

8-10

(1 mark)

(iv) Using indicator B in the left hemisphere to diagnose ASD in a sample of 100 people who are known to have ASD how many would be incorrectly identified as not having ASD on the basis of this test? (False negatives)

true positive rate 0.9

10 missed

(1 mark)

(e) Do the results of this research suggest that MRI scanning should be introduced to diagnose ASD? Suggest advantages and disadvantages of using this method compared to alternatives such as interviews or administering cognitive tests.

less subjective than interview or testing

not totally accurate

false positive and false negative rate

all brains are different so hard to standardise

very small sample/only 20

may not apply to whole population

useful in conjunction with other tests

expensive

unpleasant

(3 marks) (HSW Aa, Bf)

Total 16 marks

December 2010

Page 1 ©The Nuffield Foundation, 2010

Copies may be made for UK in schools and colleges

A2 Science In Society 3.3 Student sheets

Introduction

Autism is a severe developmental disorder particularly affecting the ability to relate to other people. It usually diagnosed in the first few years of a child’s life. The cause is not known. Earlier theories which blamed poor parenting are now known to be wrong. Recently there has been a sharp increase in the number of cases of autism in the UK, as shown in Figure 1.

data from Rate of first recorded diagnosis of autism and other pervasive developmental disorders in United Kingdom general practice, 1988 to 2001: Liam Smeeth et al

Most other countries, including the USA, Japan and Australia, have shown similar increases over the same period of time. There is no agreed explanation for the increase.

Two types of explanation have been put forward to account for the changes shown in Figure 1.

Explanation A – The true incidence is rising and this is due an environmental cause. The MMR vaccine has been suggested as one such cause.

Explanation B – The rise in incidence does not reflect a change in the number of people with developmental disorders. It is due to increased surveillance and to a broadening of the definition of autism, to include those with milder forms such as Asperger’s. The disease is now known as autism spectrum disorder, ASD.

(a) (i) This is an example of evidence often used in arguments to support explanation A:

“There has been a ten-fold increase in autism and related forms of brain damage in the last 15 years, roughly coinciding with MMR’s introduction.”

Explain what is wrong with an argument to support explanation A based on this evidence.

(2 marks)

(ii) Suggest one other environmental factor that might affect brain development in some way.

(1 mark)

(b) In 1994 DSM-IV replaced DSM-III. DSM is the manual, used by most doctors, that gives criteria used to diagnose many mental illnesses, including autism. DSM-IV changed the criteria to include the milder ASD. Suggest and explain two reasons why diagnostic criteria change over time.

(2 marks)

(c) In order to test explanation B researchers re-interviewed and re-tested 20 adults who had been diagnosed with mental retardation and developmental language disorder as children.

The researchers found that at least 34% of these would now be diagnosed as having autism spectrum disorder, ASD.

Explain how this finding could be used to support explanation B.

(2 marks)

(d) One attempt to improve diagnosis of autism is by the use of MRI scans of the brain. Researchers found that the brains of those with ASD showed some characteristic features in parts of the cortex. These features included differences in the thickness and folding, of the cortex compared with controls. The researchers taught a computer to classify brain scans according to five of these features, using 20 ASD subjects and 20 controls.

Figure 2 shows how the computer performed in diagnosing ASD on the basis of the 5 features B, C, D, E and F.

Figure 2., Graphs for the five discrete features, in the left hemisphere (X), and in the right hemisphere (Y). Individual points on the graph depict classifications on the basis of different features B -F represent other features.

(i) What is the false positive rate for feature F in the left hemisphere?

(1 mark)

(ii) Considering the five features B – F in both the left and right hemispheres, which would provide the most reliable indicator of an ASD diagnosis? Justify your answer.

(3 marks)

(iii) Using only indicator B in the left hemisphere to diagnose ASD in a sample of 100 people without ASD how many would be incorrectly identified as being affected by ASD? (False positives)

(1 mark)

(iv) Using indicator B in the left hemisphere to diagnose ASD in a sample of 100 people who are known to have ASD how many would be incorrectly identified as not having ASD on the basis of this test? (False negatives)

(1 mark)

(e) Do the results of this research suggest that MRI scanning should be introduced to diagnose ASD? Suggest advantages and disadvantages of using this method compared to alternatives such as interviews or administering cognitive tests.

(3 marks)

Total 16 marks

Page 1 ©The Nuffield Foundation, 2010

Copies may be made for UK in schools and colleges