Slide 1OUTLINEDirect ObservationDirect Observation SystemSlide 5Evolution of Objective MonitoringPedometersPedometersExample – America on the move study in US adultsAmish individualsAccelerometersSlide 12Expanding memory capacitySlide 14Translating counts into METsAdvances: machine learningNHANES data – activity from accelerometersSlide 18NHANES data – sedentary behavior from accelerometersAccelerometersCommercial devicesSlide 22Accuracy and precisionAccuracy and precisionAccuracy/precision exampleSources of errorEstablishing quality of exposure measuresSummary of measurementSummaryObjective Physical Activity Measurement Fall 2017OUTLINE•Direct observation•Wearable devices•Meaning from monitors•Measurement errorQuestion:What are some characteristics about a person’s physical activity that may be related to health outcomes? -VO2 max-intensity -Duration -TypeDirect Observation•Individual observer monitoring a person for a set period of time•Used now to validate other measures•Get duration, intensity, posture, context•Useful for monitoring certain populations: i.e children and adolescentsDirect Observation System•Focal Sampling and Duration CodingObserver XT and Pocket ObserverLocationHome IndoorHome OutdoorWork/SchoolCommunity Body position•lying •sitting•standing still•standing still with upper body movement•standing/moving•moving-moderate (> 3 METS)•moving-vigorous (> 6 METs)Function•Home Activity•Office work•School•Leisure•Lawn/garden•Self-care•Transportation•MiscellaneousStrengths/weaknessesStrengthsdetailed information, multiple dimensionsaccuracyassessment of free livingused as a validation tool Weaknessimpractical for large populationsreactivity-change behavior because you know you are being watched time consuming extensive training for the observer has some subjectivityEvolution of Objective Monitoring•All started with measuring distance walked–Ancient Romans•‘Hodometer’ of Vitruvius–Leonardo DaVinci-1667•Step counters, military–Y. Hatano -1965•Manpo-Kei – “10,000 steps meter”–Yamax, Omron, New-Lifestyles…………Pedometers•Measure steps per day– put in stride length, height, weight – some tell you about your activityPedometersAdvantages•Objective•Easy to use•Easy to interpret for researchers and subjectsDisadvantages•Do not provide valid information on–Intensity • steps/min •Do not know if it was from running, walking –Sedentary time•Not all pedometers are created equalExample – America on the move study in US adults Bassett et al., 2010Amish individualsAccelerometers•Measure body movement in terms of acceleration–Pizoelectric sensors–Store data onboard- you download to computer at end of wear period•There are many different monitors available–Single-axis–Multi-sensor – up to 3 axis. Up/down, front back, side/side –Measures in counts/minute Bassett and Chen, 20055032 71647164GT71256256 KB memoryGT1M1 MB memory64 KB memory64 KB memory16 MB memory3 axesGT3X250 MB memoryRaw acceleration3 axesGT3X PlusExpanding memory capacityMonitor over long periods of timeUsing high sampling rate and raw signalDirect measurement of METs (energy expenditure) during a gardening activityActivity monitorsMeasurement of energyexpenditure using indirect calorimetryMETsActivity monitor outputUse oxygen consumption (mlO2/kg/min) and divide by 3.5 mlO2/kg/minTranslating counts into METsFreedson and Melanson, MSSE, 1998Advances: machine learning•Recognize patterns in data•Identify activities •More accurate prediction of METs•Not all activity is linear with respect to METSNHANES data – activity from accelerometersAccording to accelerometer data, the average US adult participates in:–45 minutes of moderate intensity activity/week–19 minutes of vigorous intensity activity/ week According to self-report measures: –325 minutes of moderate intensity activity/week–74 minutes of vigorous intensity activity/weekTucker et al., 2013NHANES data – sedentary behavior from accelerometersAverage = 7.7 hours or 55% of timeAccelerometersAdvantages•Objective•Easy to use•Provides time stamped data on intensity of movement•Lots of potential!!Disadvantages• many different monitors makes it hard to compare across studies •Trade off: burden vs. accuracy–How many monitors?• limited by existing processing. Not all activities follow linear trendCommercial devicesIMPORTANT CONSIDERATIONS WITH MEASUREMENT: HOW GOOD IS YOUR MEASUREMENT DEVICE?How do we evaluate the validity of our measurements & findings?Accuracy and precisionAccuracy – how close a measure is to the true value - determination of valid measurement toolPrecision – how close the repeated measures are to eachotherAccuracy and precisionAccuracy/precision exampleSources of error1) Random error = Error due to chance–Includes measurement error, biological variation–Large sample size reduces effect of random error–P-value and 95% confidence intervals–Poor precision• testing and calibration of instrumentation 2) Bias–Selection Bias: occurs when characteristics of people selected differ from those not selected (not random)–Measurement Bias: Recall bias 3) Confounding–3rd variable unequally distributed between 2 exposure groups–Example? Dietary factors can confound findings on PA and cancer–Randomization If the findings of a study were not due to any of these three sources of error then the study is internally validEstablishing quality of exposure measures1) Temporal: Timeframe (factors happen in the same time frame)–i.e. high cholesterol and CHD2) Biological Plausibility: A biological reason for the relationship –i.e. sedentary lifestyle, inflammation, atherosclerosis 3) Consistency: Relationship occurs in different populations, studies–i.e. risk factors are similar in people of European and African dissent 4) Strength of association: Two factors are not weakly related–i.e. smoking and lung cancer vs smoking and accidents 5) Dose-response: As the levels of 1 factor increases the other factor also increases (AKA “biological gradient”)6) Reversibility: when the exposure is eliminated or decreased, the outcome is eliminated or decreasesSummary of measurement•Prediction of energy expenditure is the basis of most physical activity measurement tools•There are a lot of tools available•Each of them has strengths and weaknesses. You should know what they are. •There is