2: Methods of Assessment

Question 1

What is construct validity?

Answer 1

Whether a test measures what it claims, relative to a gold standard or future outcome.

Question 2

What is ecological validity?

Answer 2

How well assessment data reflect behaviour in a natural, everyday setting.

Question 3

What does a reliable test do?

Answer 3

Produce consistent results on each administration.

Question 4

How reliable is the MMSE?

Answer 4

It shows high correlation with other cognitive tests, and moderate correlation with Activities of Daily Living assessment.

Question 5

What does sensitivity depend on?

Answer 5

The fidelity with which the test distinguishes between behavioural outcomes.

Question 6

What does sensitivity seek to identify?

Answer 6

Individuals who have a disease.

Question 7

What does specificity seek to identify?

Answer 7

Individuals who do not have a disease.

Question 8

How specific is the MMSE?

Answer 8

100%

Question 9

How sensitive is the MMSE?

Answer 9

Only 55%

Question 10

What is positive predictive value?

Answer 10

The ability to detect a disease given the results of the test.

Question 11

What does positive predictive value depend on?

Answer 11

Sensitivity, specificity and prevalence of the disease in the population.

Question 12

How is specificity calculated/

Answer 12

True neg. / (Tre neg. + False pos.)

Question 13

How is sensitivity calculated?

Answer 13

True pos. / (True pos. + False pos.)

Question 14

How is PPV calculated?

Answer 14

True pos. / (True pos. False neg.)

Question 15

Give 2 problem with false positive diasgnostics.

Answer 15

They cause unnecessary worry and the cost and side effects of unnecessary treatment.

Question 16

Give 2 problems with false negative diagnostics.

Answer 16

Failure to treat leads to symptom progression and risk of social stigma or feelings of guilt.

Question 17

What amino acid errors underlies Huntington’s disease?

Answer 17

40+ repeats of CAG.

Question 18

Give 1 advantage of genotyping.

Answer 18

Diagnostic, predictive, prenatal and even preimplantation (IVF) testing.

Question 19

Give 2 disadvantages of genotyping.

Answer 19

Ethical implications and risk of showing a predisposition rather than a disease.

Question 20

Briefly describe how CT works.

Answer 20

An X-ray beam rotates around the head and produces images of tissue density.

Question 21

Give 3 advantages of CT.

Answer 21

It is the gold standard for detecting cerebral hemorrhage in the acute phase,cheap, and widely available.

Question 22

Give 3 disadvantages of CT.

Answer 22

Low spatial resolution, ionizing radiation, and the criterion for a lesion is not entirely objective.

Question 23

Briefly describe how MRI works.

Answer 23

Magnetic fields excite hydrogen atoms and a radio wave temporarily destabilizes the alignment of these atoms.

Question 24

What is measured in MRI?

Answer 24

The time taken to return to equilibrium or the hydrogen phases.

Question 25

What type of MRI image is most sensitive to stroke?

Answer 25

Diffusion-weighted.

Question 26

What is the contrast in diffusion-tensor imaging based on?

Answer 26

The directional rate of diffusion of water molecules.

Question 27

Give 2 advantages of MRI.

Answer 27

Safe and has excellent resolution (especially on stroke sequences at high magnetic field).

Question 28

Give 3 disadvantages of MRI.

Answer 28

Cost, logistics, and the criterion for a lesion is not entirely objective.

Question 29

What does voxel-based morphology map?

Answer 29

Differences between patients and controls or within the same group over time.

Question 30

Briefly describe the VBM method.

Answer 30

Take MR images and their associated behavioural variable, normalise each one, smooth each to deal with individual differences, compare them, and output the result as a statistical map.

Question 31

Give 3 advantages of VBM.

Answer 31

It provides an objective criterion for a lesion, the model can account for variables of no interest, and the model can investigate neural correlates of continuous behavioural variables.

Question 32

What is assumption 1 of VBM?

Answer 32

Multiple brains can be averaged into a standard brain.

Question 33

What is assumption 2 of VBM?

Answer 33

There is a linear relationship between neural loss and intensity of MR image.

Question 34

What is assumption 3 of VBM?

Answer 34

Neuronal density is normally distributed in the healthy population for all brain regions.

Question 35

What is compared in VLBM?

Answer 35

Behaviour in patients with a lesion with behaviour in those without.

Question 36

What is output in VLBM?

Answer 36

A map showing voxels whose lesion is associated with a higher/lower behavioural score.

Question 37

Give 1 advantage of VLBM.

Answer 37

It makes fewer assumptions than VBM.

Question 38

Give 4 disadvantages of VLBM.

Answer 38

It is laborious, subjective, assumes that brain normalization works, and has an error of 1 - 2 cm in locating the critical area due to underlying vascular anatomy.

Question 39

Describe misery perfusion.

Answer 39

System always compensating for reduced blood flow, so no dynamic ability to increase.

Question 40

Describe luxury perfusion.

Answer 40

Destroyer tissue no longer requires blood, so regulation not require for surviving tissue.

Question 41

What is often disrupted by a stroke?

Answer 41

Hemodynamic response.

Question 42

Give 4 advantages of fMRI.

Answer 42

It’s non-invasive, has excellent spatial resolution, reasonable temporal resolution, and the whole brain can be imaged at once.

Question 43

Give 5 disadvantages of fMRI.

Answer 43

It’s expensive, noisy, no metal can be in the room, shows correlation only, and requires careful statistical analysis.

Question 44

Give 3 advantages of PET.

Answer 44

It can measure receptors, neurotransmitters, and drugs in humans.

Question 45

Give 3 disadvantages of PET.

Answer 45

It’s radioactive, expensive and logistically difficult, and the ambiguity of interpretation means it requires careful design.