NUTR 400 Part 2

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NUTR 400 Part 2
2011-11-08 00:34:45

Validity and Reliability in Estimating Intake Methods of Estimating Nutritional intake
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  1. What variables are there when choosing what method to use to estimate dietary intake? (4)
    • -whether you want information about dietary
    • behaviours or amounts of foods, nutrients, and nonnutrient
    • food constituents consumed
    • - whether you want to assess absolute or relative
    • amounts of foods and/or nutrients
    • - whether you want historical or current patterns
    • - time, resources, money etc that you hav4e
  2. What are the methods of estimating usual dietary intake? (4)
    • Food Frequency Questionaire
    • 24Hour Recall
    • Food Record
    • Direct Observation
  3. What are considered short term instruments? When are the most used?
    • - 24hr recall, food records, food diaries
    • - Oftern used in population surverys for monitoring health and nutrition
  4. What are considered long term instruments? When are the most used?
    • - FFQ
    • -Often used in large cohort or case control studies to examine die health relationships
  5. What are some variable approached to using fooddiaries/ records? (4)
    • - Trained or untrained respondents
    • - Detailed review or not
    • - Highly standardized coding rules or not
    • - Development of electronic methods: PDA, cell
    • phones
  6. What the strengths of food diaries/ records?(4)
    • - Intake is quantified, detailed
    • - Can include weekends
    • - Could be relatively accurate (detail/training)
    • - Data are rich in details (Nutrient, Cooking practices, Meal and eating frequency)
  7. What the limitations of food diaries/ records?(7)
    • -Recording influences diet (reactive tool)- Biased measurement
    • - Requires literacy
    • - High respondent and investigator burden
    • - Multiple days required to estimate usual intake
    • - Sample selection bias
    • - Completion worse over time
    • - Underreporting is typical- Worse with overweight/obese
  8. What is a 24 Hour Recall?
    • -Ascertain descriptions and amounts of foods consumed
    • in 24 hour period prior to interview
    • - Can be interviewer administered or self-administered by computer (US National Cancer Institute is developing a
    • web-based tool;
  9. What are some variable approached to using 24 hour recalls? (8)
    • -Training of interviewers
    • - Standardization of probing questions
    • - Multiple passes through the day
    • - Computer vs. paper/pencil administration
    • - In-person vs. telephone
    • - Portion size models or measurement aids
    • - Quality and completeness of nutrient database
    • -Development of self-administered automated
    • -5 systems administered via computer or internet
  10. What the strengths of 24 hour recalls?(6)
    • -low respondent burden and high compliance- less
    • chance of selection bias due to burden
    • - can be suitable for illiterate subjects
    • - standardised protocol can be used
    • - unlikely to interfere with dietary behaviour
    • - can get through relatively large numbers of subjects in
    • one day
    • ! can get details on cooking practises, brands, meal
    • frequency etc.
  11. What the limitationss of 24 hour recalls?(6)
    • -Imperfect knowledge and memory- relies on this
    • - Relies heavily on getting a portion size estimation
    • - Multiple days required to estimate usual intake- single day is a snap-shot
    • - Costly to administer if face-to face- Highly trained interviewers
    • - Some evidence that reporting declines with multiple administrations
    • - Underreporting is typical- Worse with overweight/obese
  12. Disadvantages of 24 hour recalls (3)
    • - relies heavily on memory
    • - portion size estimation issues
    • - a single 24 hour recall only gives a snapshot of that
    • persons intake
    • (simply having a bad day cannot be used to make judgements that person likely nutrition status
  13. What are some variable approached to using FFQ? (8)
    • - Number of foods, clarity of questions
    • - Portion size questions: pictures vs. text description
    • - Time frame
    • - Development of food list, nutrient database
    • - Type of administration: computer vs. paper
    • - Specificity to population of interest
    • - Supplement intake
    • - Food preparation
  14. FFQ Strengths (4)
    • -Can assess intakes of very large numbers of people
    • (can be distributed/collected by mail and self
    • administered)
    • -Atempts to estimate 'usual' individual intake of foods with one administration
    • - Does not affect eating behavior-
    • -Lower cost of administering/processing-optic-readable scanned forms and Computer-generated data
  15. FFQ: limitations (8)
    • - Lack details ( finite food list, details of cookin methods, specific food type lost
    • -Cognitively complex
    • - Requires literacy
    • - Affected by recent diet
    • - Severe measurement error: prone to bias
    • - Different FFQs can behave quite differently-FFQ designed to
    • assess calcium intake is NOT appropriate if you want to
    • measure intakes of fruit and vegetables
    • - Different populations respond differently
    • -Problems with assessing foods
  16. How to assess a FFQ? (4)
    • 1. What was the original purpose of the
    • questionnaire?
    • 2. Who was the target population? Are
    • questionnaires developed in Europe suitable for
    • use in Canada?
    • 3. When was the questionnaire developed? Are the
    • foods and portion sizes still relevant?
    • 4. Has a previous validation been carried out, was it acceptable
  17. How to analyze food records/recalls?
    What questions/ limts are there with this method of analysis?
    • Databases ( USDA, CANDI)
    • Questions:
    • Foods away from home?
    • Foods prepared at home?
    • Fortified/enriched foods?
    • How good is it at accurately determining nutrients?
    • Updating of the systerm with changes to food supply?
    • New food compound of health interest?
    • Supplement use?
  18. When reading literature what consideration should you make when analyzing food estimation? (3)
    • - What database was used?
    • - Are valid estimates possible - intake data collected to obtain a reliable and valid estimate of food in the population of interest., completion of the database
    • -Is the correction level of precision reported
  19. How are dietary patterns measured?
    • - Used to assess dietary intake (food records, FFQ)
    • for case-control, survey & cohort studies
    • - Cluster, Factor or Index analysis
    • - Cluster & Factor determine patterns from collected
    • food intake
    • - Indexes are pre-determined based on definition of
    • healthy eating
    • - Healthy Eating Index, Dietary Quality Index,
    • Alternate Healthy Eating Index
    • -limitations in using these?
  20. What are the limitations of biomarkers used in nutrition studies?
    • -Very few short term available, few long term
    • EXAMPLES: see readings
    • - Concentration: reflect the biological response to intake - Cannot be used to assess amount consumed, Correlate to amount consumed, May reflect short or long term intakes, Some are appropriate for risk assessment
    • -Most nutrients tightly controlled: no relationship to intake
  21. What are some innovations in estimating intake (5)
    • -Web-based, automated FFQs
    • - Self-administered, automated, web-based,
    • 24-hour dietary recalls
    • - Real time data collection of food records
    • - Voice recognition software
    • - Combining methods: FFQ with 24-hour recalls
  22. What is External Validity?
    How is it increased? (2)
    • study design)- extent to which results from a study can be extended to universe that is broader than population
    • studied.
    • Increased by:
    • a) subject selection - random selection, differences in confounding recruitment methods (including incentives)
    • b) subject number - sufficient statistical poer to detect differences between groups

    • -- Still need quality control of measures and judgment
    • about degree to which results can be extrapolated
  23. What is internal Validity?
    • adequacy of measurement - how well does it measure what it is intended to measure (index or indicator reflects what it is intended to
    • measure)
  24. Components of internal validity (4) and how they are affected
    • 1) Reliability (reproducibility)- Degree to which repeated measures give same value
    • -Affected by:
    • a) True variation in the measurement
    • b) Random error (or random variation)
    • c) Systematic errors
    • 2) Face Validity - judgment (often by experts) that tool measures what it is supposed to
    • 3) Content Validity - are all components of the
    • construct (e.g. diet) measured by the tool?
    • 4) Criterion validity - how well the tool performs
    • compared with another tool (gold standard?) known
    • to measure the same thing?
  25. How to ensure internal validity? (4)
    • 1) Reliability
    • - Standardize protocols; calibrate instruments
    • - Use protocols suitable for situation
    • - Include test-retest as part of study design
    • 2) Get expert opinion before implementing tool
    • 3) Conceptualize content of construct and choose tools accordingly (e.g. based on literature)
    • 4) Compare between and among tools
  26. When does changing a tool change the validity of your measures? How might you minimize the likelihood that changed to you method have been invalidates** EXAM
    - How to make you tools still useful
  27. What is a confounding variable?
    How can you control this? (2)
    A special type of bias (therefore affects validity)1 A characteristic or variable that is distributed differently in the study and control groups, and affects the outcome being assessed. Eg. (Randomization, stratification)

    • Ways to control
    • 1) study design - randomization, stratificaton, recruitment restirction, matching
    • 2) Post Data Collection - stratification (in analysis) - multivariate analysis
  28. Validity measures diary /food record (2)
    • -complete and accurate record of all food consumed, where the choice of food consumed has not been influenced by the act of recording
    • Valid FFQ
    • - accurate reflection of typical food intake over
    • a designated period of time - undistorted by false memory or desire to appear "norma"
  29. What is a measuresment error?
    Difference between the true value and the value obtained from a measurem
  30. What is a systematic error (bias)?
    What is negative bias and positive bias?
    -Source of error in which measurements consistently depart from the true values ( if a instrument has a systematic error then the average of many repeat measures does not approximate the true value)

    • Bias is either negative or positive
    • 1)Negative bias - means that dietary intakes are
    • systematically under-estimated
    • 2) Positive bias - means that dietary intakes are
    • systematically over-estimated

    • Eg. Doubly labelled water studies suggest that obese
    • people are likely to systematically under-report
    • energy intake
  31. What is Random Error (5)?
    • -Unpredictable error
    • affects reproducibility (or precision) of a method
    • - caused by true variation in intake + measurement error
    • - reduces the strength of associations observed between diet and markers for disease
    • - reduces the statistical power of studies
  32. What is precision?
    How valid it is in nutrition studies
    • The ability of a measurement to be reproduced - i.e.
    • produces the same answer on repeat administrations

    • -Almost impossible to achieve at the individual level food intake varies widely over time
    • i.e. if you did 24 hour recalls on 1 person on 4
    • different occasions, you would be unlikely to get
    • exactly the same energy and nutrient intakes on each
    • occasion
  33. What are the major sources of measurements of error (9)
    • 1) Respondent error: either random or systematic
    • OR inability/unwillingness to comply with protocols
    • 2) Interviewer bias:
    • - Monday interview vs friday, interviewers with desires to promote healthy eating may obtain biased results, interviewed may not click with certain individuals but have very good rapport with others
    • 3) Respondent memory lapses
    • -use memory aids (e.g. food models, photographs)
    • - not such a big problem if the time period between food intake and recall of the intake is short
    • - foods contributing to the main part of the meal are remembered better than minor or odd foods
    • 4) Incorrect estimation of portion size
    • - probably a large source of measurement error
    • -using average portion weight instead of a estimate can result in substantial error
    • 5) Honest vs desirable responses
    • 6) Foods served vs foods consumed
    • 7) Subject characteristics (obesity, age,
    • motivation, etc)
  34. What influences random (1) and systematic errors (3)
    • Random error- within person error
    • Systematic error- Person-specific bias
    • - Constant additive error
    • - Intake-related bias
  35. How can you get coding and computation errors (4)
  36. - Can arise from poor descriptions of foods
    • - Inaccurate conversion from estimates or household measures to actual weights
    • - May not have appropriate tables for food composition data
    • - Systematic mistakes when entering data - e.g. entering data - eg. orange juice as concentrated OJ can result in vitamin C estimates 5x greater than they should be