W5 - Measurement of sedentary behaviour

Question 1

Why do we measure sedentary behaviour?

Answer 1

• used in a wide variety of contexts and settings
• shows links between sedentary behaviour and health
• Populations surveillance work
• Encourages interventions & reduce peoples sitting time
• More difficult for people to measure sitting time than PA(usually structured in a person’s day)

Question 2

Define these key measurement terms:
* Reliability
* Validity
* Criterion/concurrent validity
* Convergent validity

Answer 2

• the consistency or repeatability of a measurement
• the degree of truthfulness of a test score, does a test/tool measure what it is supposed to measure
• measures how well a new test/tool compares to a ‘gold standard’ measure of the same construct
• the extent to which the output of a test/tool is associated with that of another instrument which intends to measure the same exposure/construct of interest (used in the absence of a criterion measure)

Question 3

Describe the ActivPAL inclinometer(accelerometer)

Answer 3

• Determines posture on the basis of thigh inclination, classifies activity into time spent sitting/lying, standing, stepping, stepping cadence, number of steps taken and sit-to-stand and stand-to-sit transitions
  
  • a valid measure of sitting time, when validated against direct observation
  • Picks up the orientation of the thigh(strapped to anterior portion of the thigh)
• MOST reliable & valid measurements
  
  • Not waterproof, uncomfortable to remove the plaster all the time
• £300 per unit

Question 4

Describe the ActiGraph accelerometer

Answer 4

• Detects vertical accelerations of the hip
• records integrated acceleration data, traditionally associated as a measure of PA
  
  • Not directly measure posture - only estimate movement time
  • data is presented in the form of movement counts
  • More accurate report of sedentary time than questionnaires

Question 5

Compare the ActivPAL to the ActiGraph

Answer 5

• ActivPAL was more superior to the ActiGraph at measuring sedentary behaviour
• Most common complaint with the activPAL is skin irritation
  Compliance to the ActivPAL was very poor(not worn for the required amount of time)

Question 6

Describe the GENEActiv accelerometer

Answer 6

• Worn on wrist or thigh
  
  • Uses ‘Sedentary Sphere’ to identify sedentary behaviours
  • Angle of the wrist can help identify when the person is sedentary(3 different planes) - not very accurate

Question 6

Explain the ‘Sedentary Sphere’ method

Answer 6

• Describes possible outputs based on wrist rotation and elevation
  
  • Elevations >15° below the horizontal indicate the wrist is elevated, if activity intensity is low, this indicates a sitting or reclining posture
  • Elevations >15° below the horizontal indicate that the arm is hanging more vertically, this indicates a standing position
  • Estimates could be better than self-reported data

Question 7

What is an axivity accelerometer?

Answer 7

• Worn on wrist or thigh (and back, can determine the orientation of the back, sitting/standing)
  
  • samples raw measurement data

Question 8

What are the advantages of using device based measurements?

Answer 8

• Provides a more objective measure
• Does not rely on participant recall
• Provides time-stamped data
• Less burden for participants
• Captures all forms of behaviours, plus sleep

Question 9

What are the disadvantages of using device based measurements?

Answer 9

• Can be expensive
• Relies upon specific software
• Inconsistencies in data reduction methods
• Compliance issues
• Some devices are not waterproof
• Does not provide contextual information

Question 10

What are self-report measures?

Answer 10

• Earlier research assessing sedentary behaviour primarily focussed on TV viewing time
• Participant asked to report their total time spent watching TV and/or videos in the last 7 days (excluding times when the TV was on, but individuals were doing something else, e.g. household chores)
• Low validity

Question 11

What results can be seen when comparing domain-specific to single-item data?

Answer 11

• Comparisons made between domain-specific and single-item measured sitting time in adults
  
  • People drastically underestimate their sitting time
  • For big populations, domain specific questionnaires are probably more reliable

Question 12

What are the advantages of self-report methods?

Answer 12

• Inexpensive
• Quick to administer
• Low participant burden
• Useful for population studies
• Provides contextual information

Question 13

What are the disadvantages of self-report measures?

Answer 13

• Population specific
• Memory is a concern, reporting biases
• Standardisation issues
• Tendency to miss breaks in sedentary time
• Earlier self-report measures have solely focussed on TV viewing time