Lecture 7: Validity, Accuracy, Sensitivity and Friends Flashcards

1
Q

What is validity?

A

The extent to which a method gives you the “correct” answer i.e. measures what you want it to measure

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2
Q

What is absolute validity?

A

the extent to which a measurement or method accurately reflects the true value or reality of what it is intended to assess, without bias or error

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3
Q

What does the reference method require for absolute validity?

A

Reference method requires discreet or hidden observation or recording of what a person consumes, without their awareness, to ensure accurate and unbiased data

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4
Q

What is relative validity?

A

the degree to which the results of one measurement or method agree with those of a reference or gold-standard method, rather than directly reflecting an absolute true value

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5
Q

What is the reference method for relative validity?

A

Reference method is another indirect method of assessing intake

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6
Q

What is repeatability?

A

The extent to which a method gives you the same answer each time you use it

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7
Q

What are issues to consider in an FFQ “validation” study?

A
  • Appropriate reference method
  • Study sample
  • Timeframe
  • Methods
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8
Q

What is accuracy?

A

Describes the extent to which the measurement is close to the true value

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9
Q

What is measurement error?

A

Difference between measured value and true value

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10
Q

What is the observed intake equation?

A

observed intake = true intake + measurement error

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11
Q

What are the two types of measurement error?

A
  • Random error
  • Systematic error
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12
Q

What does measurement error lead to?

A
  • Attenuation of relationships
  • Bias
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13
Q

What is random error due to?

A

Chance or normal variation

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14
Q

What does’t random error change?

A

The mean

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15
Q

What does random error increase?

A

Variability around the mean (stretches the tails)

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16
Q

What does random error decrease?

A

Reproducibility

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17
Q

What are the main sources of random error?

A
  • Daily variation in consumption
  • Inaccurate portion size estimation
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18
Q

Can we remove random error?

A

Can’t remove totally

19
Q

What does systematic error change?

A

The mean - causes results to depart from true value in consistent direction (=bias)

20
Q

What does systematic error decrease?

A

Validity

21
Q

What are the main types of systematic error?

A
  • Selection bias (non-representative sample)
  • Measurement bias (incorrect calibration)
22
Q

Can systematic error be removed?

A

Can’t be removed by statistical analysis

23
Q

What is non-response bias?

A

When a specific subset of people:
- don’t volunteer to participate
- don’t adhere to intervention
- drop out

24
Q

Non-response bias makes the sample…

A

Non-representative

25
Q

What are stratagies to remove non-response bias?

A
  • Minimize respondent burden
  • Reminders
  • Offer rewards
  • Train interviewers
  • Identify non-responders
  • Over-sample groups at risk of non-responding
26
Q

What is respondent bias?

A

Bias introduced by the respondent

27
Q

What are the three main types of respondent bias?

A
  • Low energy reporting
  • Over reporting
  • Social desirability and approval biases
28
Q

What are stratagies to reduce respondent bias?

A
  • Pre-test method improvements
  • Interviewer training
  • Private interviews
  • Identify flawed data
  • Identify participants at risk
29
Q

What is interviewer bias?

A

Bias introduced by the interviewer

30
Q

What can interviewer bias be caused by?

A
  • Incorrect recording
  • Intentional omissions
  • Poor cultural sensitivity
31
Q

What are stratagies to avoid interviewer bias?

A
  • Standardised computer interviews
  • Train interviewers
  • Identify problem interviewers
32
Q

What are respondent memory lapses?

A

Errors of omission and commission (forgotten so lie instead)

33
Q

When may respondent memory lapses be more likely?

A
  • Longer time period to be recalled
  • Men
  • Age extremes
  • Distracting environment
34
Q

What are stratagies to avoid respondent memory lapses?

A
  • Multiple pass interviewing techniques (interrupted recall, probe questions)
  • Minimize time between intake and recall
  • Work with information retrieval (visualisation)
35
Q

What is probably the largest source of error in dietary assessments?

A

Incorrect portion estimation

36
Q

What is incorrect portion estimation?

A

Failure to accurately quantify amount eaten

37
Q

When does incorrect portion estimation vary?

A

With type and size of food

38
Q

What are stratagies to decrease incorrect portion estimation?

A
  • Measurement aids
  • Train interviewers
  • Train respondents
39
Q

Why is omission of supplements common?

A
  • No uniform definition of a supplement
  • No standard method to collect supplement data
40
Q

What does omission of supplements lead to?

A
  • Systematic underestimation of nutrient intake
  • Overestimation of prevalence inadequacy
41
Q

What are stratagies to avoid omission of supplements?

A
  • Structured questionnare on long-term intake
  • Questions on: brand, amount, frequency, duration of use, chemical form
  • Interviewer sights supplement
42
Q

What is sensitivity?

A

How good the test/method is at correctly identifying people who have the disease/low status

43
Q

What is specificity?

A

How good the test/method is at correctly identifying people who are well/have adequate status