2: Methods of Assessment Flashcards
What is construct validity?
Whether a test measures what it claims, relative to a gold standard or future outcome.
What is ecological validity?
How well assessment data reflect behaviour in a natural, everyday setting.
What does a reliable test do?
Produce consistent results on each administration.
How reliable is the MMSE?
It shows high correlation with other cognitive tests, and moderate correlation with Activities of Daily Living assessment.
What does sensitivity depend on?
The fidelity with which the test distinguishes between behavioural outcomes.
What does sensitivity seek to identify?
Individuals who have a disease.
What does specificity seek to identify?
Individuals who do not have a disease.
How specific is the MMSE?
100%
How sensitive is the MMSE?
Only 55%
What is positive predictive value?
The ability to detect a disease given the results of the test.
What does positive predictive value depend on?
Sensitivity, specificity and prevalence of the disease in the population.
How is specificity calculated/
True neg. / (Tre neg. + False pos.)
How is sensitivity calculated?
True pos. / (True pos. + False pos.)
How is PPV calculated?
True pos. / (True pos. False neg.)
Give 2 problem with false positive diasgnostics.
They cause unnecessary worry and the cost and side effects of unnecessary treatment.
Give 2 problems with false negative diagnostics.
Failure to treat leads to symptom progression and risk of social stigma or feelings of guilt.
What amino acid errors underlies Huntington’s disease?
40+ repeats of CAG.
Give 1 advantage of genotyping.
Diagnostic, predictive, prenatal and even preimplantation (IVF) testing.
Give 2 disadvantages of genotyping.
Ethical implications and risk of showing a predisposition rather than a disease.
Briefly describe how CT works.
An X-ray beam rotates around the head and produces images of tissue density.
Give 3 advantages of CT.
It is the gold standard for detecting cerebral hemorrhage in the acute phase,cheap, and widely available.
Give 3 disadvantages of CT.
Low spatial resolution, ionizing radiation, and the criterion for a lesion is not entirely objective.
Briefly describe how MRI works.
Magnetic fields excite hydrogen atoms and a radio wave temporarily destabilizes the alignment of these atoms.
What is measured in MRI?
The time taken to return to equilibrium or the hydrogen phases.
What type of MRI image is most sensitive to stroke?
Diffusion-weighted.
What is the contrast in diffusion-tensor imaging based on?
The directional rate of diffusion of water molecules.
Give 2 advantages of MRI.
Safe and has excellent resolution (especially on stroke sequences at high magnetic field).
Give 3 disadvantages of MRI.
Cost, logistics, and the criterion for a lesion is not entirely objective.
What does voxel-based morphology map?
Differences between patients and controls or within the same group over time.
Briefly describe the VBM method.
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.
Give 3 advantages of VBM.
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.
What is assumption 1 of VBM?
Multiple brains can be averaged into a standard brain.
What is assumption 2 of VBM?
There is a linear relationship between neural loss and intensity of MR image.
What is assumption 3 of VBM?
Neuronal density is normally distributed in the healthy population for all brain regions.
What is compared in VLBM?
Behaviour in patients with a lesion with behaviour in those without.
What is output in VLBM?
A map showing voxels whose lesion is associated with a higher/lower behavioural score.
Give 1 advantage of VLBM.
It makes fewer assumptions than VBM.
Give 4 disadvantages of VLBM.
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.
Describe misery perfusion.
System always compensating for reduced blood flow, so no dynamic ability to increase.
Describe luxury perfusion.
Destroyer tissue no longer requires blood, so regulation not require for surviving tissue.
What is often disrupted by a stroke?
Hemodynamic response.
Give 4 advantages of fMRI.
It’s non-invasive, has excellent spatial resolution, reasonable temporal resolution, and the whole brain can be imaged at once.
Give 5 disadvantages of fMRI.
It’s expensive, noisy, no metal can be in the room, shows correlation only, and requires careful statistical analysis.
Give 3 advantages of PET.
It can measure receptors, neurotransmitters, and drugs in humans.
Give 3 disadvantages of PET.
It’s radioactive, expensive and logistically difficult, and the ambiguity of interpretation means it requires careful design.
