Methods for assessing psychological dysfunction Flashcards
What are the criteria for a valid assessment?
Validity, Reliability, Sensitivity, Specificity and positive predictive value
What are the two types of validity?
Construct validity - measures what it claims to measure
Ecological validity - How assessment data reflects behaviour in a natural, everyday setting
What is reliability? What are the two types?
Ability to produce consistentn results on administration
Inter-rater
Test-test
What is sensitivity?
Able to correctly identify individuals who have a disease
- fidelity with which the test distinguishes behavioural outcomes
What is a specific test?
Can correctly identify patients who do not have the disease
What is positive predictive value?
Ability to detect a disease given the results of the test - depends on sensitivity and specificity but also prevalence of disease in the population
What is the Mini-Mental State Examination (MMSE)?
- Questions with a score attached (such as where are we now, naming objects)
- Some spatial tasks (e.g copying a figure)
- If score is below 24 indicates mental deterioration
How does the MMSE do in terms of validity?
Well
- Correlation of >0.6 with other cognitive tests
- Correlation of >0.4 with daily living activities
- Longitudinal studies show point decrease 2-3 a year
How does the MMSE do in terms of sensitivity and specificity?
Not well
- All controls obtain normal scores
- However 45% of patients with mild dementia also have a normal score
How are
- sensitivity
- specificity
- positive predicted value calculated?
- sensitivity = true positive /(true positive + false negative)
- Specificity = True negative / (true negative + false positive)
- = True positive / (true positives + false positive)
What problems arise when a patient is given a false positive?
May result in unnecessary worry and treatment
What problems arise when a patient is given a false negative result?
- Feelings of guilt
- Treatment not administered to stop disease progression
What is Huntignton’s disease?
- Genetic disease caused by autosomal dominant gene
- First symptom is uncontrollable movement which then results in depression and mood disorder followed by memory loss
How is Huntington’s tested for?
Genetic screening looks at number of CAG repeats (if over 40 likely to be huntington’s)
What have genetic studies of depression revealed?
- 44 risk variants, with all humans carrying more or less of these genes
- Genes expressed in frontal and cingulate cortex
- Likely a constellation of variants along with environmental factors
What are the ethical implications of genetic screens?
- Prenatal screens, should people be able to abort
- Some family members may not want to know they have a genetic disease
- Insurance companies
What are the 3 main categories of imaging techniques?
Anatomical - CT, MR, VLBM, VBM
Functional - fMRI
Molecular - PET
What do CT scans produce?
Images of tissue density using X-rays
What are the advantages and disadvantages of CT scans?
Adv - Good for detecting cerebral hemorrhage - cheaper and widely available Disadv - Low spatial resolution - Radiation - Not good for lesions
Which images are most sensitive to a stroke?
Diffusion-weighted images - MRI scans
How is diffusion tensor imaging carried out and what does it show?
Shows brain structural connectivity
- Looks at directional rate of diffusion in water molecules (asymettrical in fibres)
What is voxel-based morphometry?
- Satistical procedure to contrast differences in structural MR scans on a voxel by voxel basis, allows mapping of differences in brain structure between patients and controls over time
How are voxel-based morphometries made?
- Take MR images from certain group and smooth indivdual differences to form a template
- Compare subject to group (normal distribution assumption)
What are some of the potential issues with voxel based morphometry?
- Can this account for individual differences?
- Is there a linear relationship between neuronal loss and intensity of MR image?
- Is neuronal density normally distributed in healthy populations for all brain regions?
What are the advantages of voxel based morphometry?
- Provide criterion for a lesion
- Can account for variables of no interest
How does voxel-wise lesion behavior mapping differ from VBM?
Similar to VBM however does not assumer linearity between neuronal loss and MR signal activity and uses non-paramteric statistics (does not assume normal distribution)
What are the components of VLBM?
- Measurement of a behavioural variable (e.g CoC score in spatial neglect)
- Delineate the lesion of MR scans
- Comparison of behaviour of patients with lesion and without leasion
- output map of voxels with lesions associated with lower behavioural scores
What are the disadvantages of VLBM?
- laborious
- subjective
- assumption that brain normalization works
- error in locating cortical area by 1-2 cm due to underlying vascular anatomy
What is a ‘BOLD’ signal?
- Blood oxygen level dependent
- Oxygenated haemoglobin has the same magentic properties as surrounding tissue but deoxygenated does not (measure changes in oxygenated verses deoxyhaemoglobin)
- Disrupts signal from surrounding tissue
- This is measured in fMRI
Why can fMRI analysis of a stoke be difficult?
Heamodynamic flow is often disrupted
What are the advantages and disadvantages of Positron Emission Tomography?
adv
- Can measure receptors, neurotranmitters and drugs in humans
disadv
- radioactive
- expensive and logistically difficult as tracers are short lived
- difficult interpretation, requires careful design
