Armstrong 2011 Methodology Seminar

8/3/2019 Armstrong 2011 Methodology Seminar

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Reported frequency of physical activity ina large epidemiological study:

relationship to specific activities and

repeatability over timeMEG Armstrong, BJ Cairns, J Green, G K Reeves, and V Beral

for The Million Women Study Collaborators

Cancer Epidemiology UnitNuffield Department of Clinical Medicine

University of Oxford

www.millionwomenstudy.org

THE MILLION WOMEN STUDY


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Overview


Background

Physical activity assessments in the Million Women Study

Frequency of physical activity at baseline and reportedspecific activities at follow-up

Repeatability over time of reported frequency of physical

activity at baseline

Summary

Methodological considerations


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Background Objective measures of physical activity (PA) are: Expensive

Impractical

Insensitive to seasons

Questionnaires usually used as:

Less expensive

Less likely to interfere with usual PA

Assessment of many variables with one instrument Simple to administer and score

However, questionnaires are:

Subjective

Prone to measurement error (memory, a portion of activity)



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Background


In prospective studies PA assessed at baseline often used toassess influence of PA on health outcomes during follow-up

Yet, baseline assessments might not represent actual PAduring extended follow-up periods:

Measurement errors during assessment

Change in PA behaviours over time Could lead to underestimation of associations between

baseline PA and health outcomes


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Physical activity

assessments in the Million

Women Study


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Prospective cohort study of 1.3million UK women

Recruited through 66 breastscreening clinics in 1996-2001

Mean age of 56 years (range 50-64)

1 in 4 of UK women in age range

Self-administered questionnaire atbaseline and at follow-up

The cohort



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Data collection At baseline women were asked:

How often do you do any strenuous exercise?

How often do you do any exercise? (91%) 6 frequency options

No distinction between summer/winter activity

18 655 repeat baseline questionnaires were completed 17 617 strenuous activity data repeats

12 748 any activity data repeats



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Data collection 65% response rate between baseline and follow-up

~ 3 years after baseline over 600 000 women answered: About how many hours each week do you spend doing:

housework, gardening, walking, cycling, any work orexercise causing sweating or a fast heartbeat?

Reported separately on summer/winter except for housework

589 896 responded to the activity questionnaires on bothbaseline and follow-up



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Frequency of physical activity at

baseline and reported specific

activities at follow-up


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Methods Mean estimated excess energy expenditure (EE) for

strenuous & specific activities reported at follow-up comparedacross baseline PA categories

Metabolic equivalents (METs) assigned to each activityaccording to Ainsworths Compendium1 of activities.

A MET = ratio of the metabolic rate required by a given worktask, to the standard resting metabolic rate obtained whilesitting quietly

Spearman correlation coefficients & P-values for trend

1Ainsworth BE, et al: Med Sci Sport Exer 2000, 32(9):S498-S516.



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METs Housework (3 METs), gardening (4 METs), walking (3.5

METs), cycling (8 METs), strenuous (8 METs). Limitations?

Multiplying by these gives gross metabolic cost ie.

Gross metabolic cost = resting METs cost + PA METs cost

Estimated net energy expenditure more appropriate for non-24 hour EE:

Middle aged to older - greater proportion of total PA composedof low intensity activities



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Why estimated net energy expenditure? One example:

Person A:does no vigorous activity in a week (0)

Person B:does one hour of vigorous activity in a week (1)

Using Ainsworths multiplier of 8:

Person A:estimated at 0x8 MET hours (0)

Person B:estimated at 1x8 MET hours (8)

But, person A expended resting MET value of 1 duringsame time period a discrepancy. Use 7 instead of 8, to

account for resting EE



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Why estimated net energy expenditure? Another example:

Person A:does one hour of housework in a week

Person B:does one hour of cycling in a week

Ainsworths multiplier is 3 for housework and 8 for cycling:

Person A:

proportion of EE attributed to resting metabolic rate = 33%

Person B:

proportion of EE attributed to resting metabolic rate = 12.5%



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Excess MET-hours for activity at follow-up in relation to baseline frequency ofstrenuous activity


Hours and excess MET-hours per week spent doing various activitiesreported ~3 years after baseline

Strenuous activity Aggregate of various activities

Freq of strenuous PAreported at baseline

Number ofwomen

hoursmean

MET-hoursmean (SD)

hoursmean

MET-hoursmean (SD)

Never 261,857 0.8 5.6 (21.3) 21.7 52.4 (39.0)

< Once per week 79,962 1.1 7.8 (20.2) 22.7 57.3 (38.0)

Once per week 115,573 1.5 10.7 (20.5) 23.4 61.5 (38.5)

2 to 3 times per week 96,415 2.4 16.5 (25.0) 24.8 69.5 (42.5)

4 to 6 times per week 19,394 3.4 23.9 (34.1) 27.2 81.3 (50.6)

Daily 16,431 3.5 24.3 (50.8) 31.1 90.6 (69.1)

Correlation coefficient 0.37 0.12 0.22

P for trend< 0.0001 < 0.0001 < 0.0001


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Hours and excess MET-hours per week spent doing various activitiesreported ~3 years after baseline

Strenuous activity Aggregate of various activities

Freq of any PAreported at baseline

Number ofwomen

hoursmean

MET-hoursmean (SD)

hoursmean

MET-hoursmean (SD)

Never 107,346 0.8 5.8 (24.5) 21.0 50.3 (41.4)

< Once per week 49,073 0.9 6.6 (21.2) 20.6 50.9 (37.8)

Once per week 92,317 1.2 8.1 (19.5) 21.3 53.9 (37.0)

2 to 3 times per week 149,138 1.6 11.4 (20.6) 22.7 60.0 (37.5)

4 to 6 times per week 57,585 2.0 13.8 (24.0) 24.2 66.0 (39.6)

Daily 134,437 1.7 12.0 (30.0) 27.0 71.2 (49.0)

Correlation coefficient 0.17 0.17 0.22

P for trend < 0.0001 < 0.0001 < 0.0001

Excess MET-hours for activity at follow-up in relation to baseline frequency ofany activity


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Hours and excess MET-hours per week spent doing various activities reported ~3years after baseline

walking cycling gardening housework

Baseline reported freqof strenuous PA

hoursmean

MET-hoursmean (SD)

hoursmean

MET-hoursmean (SD)

hoursmean

MET-hoursmean (SD)

hoursmean

MET-hoursmean (SD)

n = 589,632 n = 589,632 n = 589,632 n = 589,632

Never 3.9 9.7 (12.8) 0.1 0.9 (5.7) 2.4 7.3 (9.9) 14.4 28.8 (23.0)

< Once per week 4.4 11.1 (12.1) 0.2 1.5 (6.8) 3.1 9.4 (10.8) 13.8 27.5 (21.2)

Once per week 4.8 12.0 (12.4) 0.3 1.9 (7.7) 3.3 9.8 (11.0) 13.5 27.0 (21.1)

2 to 3 times per week 5.2 13.1 (13.2) 0.4 2.8 (9.8) 3.5 10.5 (12.1) 13.3 26.6 (21.0)

4 to 6 times per week 5.9 14.8 (14.9) 0.6 4.4 (13.1) 3.8 11.4 (13.9) 13.4 26.7 (21.6)

Daily 7.5 18.6 (20.4) 0.6 4.4 (16.5) 4.1 12.3 (15.7) 15.4 30.9 (25.7)

Correlation coefficient 0.18 0.15 0.15 -0.03

P for trend < 0.0001 < 0.0001 < 0.0001 < 0.0001

Various reported physical activities at follow-up in relation to frequency of

strenuous activity at baseline


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Hours and excess MET-hours per week spent doing various activities reported ~3years after baseline

walking cycling gardening housework

Baseline reported freqof any PA

hoursmean

MET-hoursmean (SD)

hoursmean

MET-hoursmean (SD)

hoursmean

MET-hoursmean (SD)

hoursmean

MET-hoursmean (SD)

n = 589,896 n = 589,896 n = 589,896 n = 589,896

Never 3.2 7.9 (12.7) 0.1 0.6 (4.9) 2.2 6.7 (9.8) 14.7 29.3 (23.7)

< Once per week 3.3 8.2 (11.2) 0.1 0.9 (4.7) 2.6 7.9 (9.8) 13.7 27.3 (21.8)

Once per week 3.7 9.2 (11.3) 0.2 1.3 (6.1) 2.8 8.4 (10.0) 13.5 27.0 (21.6)

2 to 3 times per week 4.4 11.0 (11.5) 0.3 1.8 (7.6) 3.0 9.1 (10.6) 13.4 26.8 (20.8)

4 to 6 times per week 5.2 13.0 (12.1) 0.4 2.7 (9.1) 3.2 9.6 (11.2) 13.5 27.0 (20.5)

Daily 6.5 16.3 (15.9) 0.4 2.6 (10.9) 3.6 10.8 (13.0) 14.8 29.6 (23.3)

Correlation coefficient 0.31 0.11 0.14 0.01

P for trend < 0.0001 < 0.0001 < 0.0001 0.002

Various reported physical activities at follow-up in relation to frequency of any

activity at baseline


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Comments Older populations more sedentary might see

decreased between person variability

Measurement error may as proportion of PAcomprised of light intensity activities increases

Social desirability bias may influence accuracy of datafrom PA questionnaires

All may reduce power of a PA instrument to discriminate



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Domestic activities = PA Do people consider housework when asked about PA?

Domestic activities = large proportion of PA in middle agedand older. Eg. British women 60-791:

Without domestic activities only 21% met PArecommendations

With domestic activities >2/3rds met recommendations

Physical impairments may report never active but stillactually do domestic activities?


1Lawlor DA, et al., J Epidemiol Community Health 2002, 56:473-478.


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Repeatability over time of

reported frequency of

physical activity at baseline


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Methods Distributions across PA categories by time between first and

repeat response

Distributions of change in PA by time between first andrepeat response

PA ordinal kappa coefficient with quadratic weighting usedto assess agreement (equivalent to intraclass correlation1)

Differences according to seasonality

1Fleiss JL, Cohen J. Educ psychol meas 1973,33:613-619.



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Distribution of reported frequency of PA by time between first and repeat

baseline questionnaires


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Distributions of changes in reported PA frequency by time between first and

repeat baseline questionnaires


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Population level vs Individual PA

Distribution similar at population level BUTAgreementbetween individuals decreases eg.

Australia 1 (45-50 yrs): 14% PA, 12% PA, over 3 yrs

Netherlands 2 (20-59 yrs): 45% changed PA level over 10-yearperiod, equal distribution between decreasers and increasers

UK 3 (33 yrs): ~1/3 and ~1/3 their PA level over an 8-year

USA 4 : 16% PA, 12% PA, over 4 yrs


1 Guthrie J. Acta Obstet Gynecol Scand 2002, 81:595-602.2 Picavet HSJ et al., Med Sci Sport Exer 2010, 43(1):74-79.

3 Parsons TJ, et al., Eur J Clin Nutr 2005, 59:49-56.4 Eaton CB et al., Am J Prev Med 1993, 9(4):209-219.


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Number

of women

Absolute

Agreement

Kappa (95% CI)

with quadraticweighting

Time between completing identical questions onfreq of strenuous PA (avg time between the two)

6 months (0.3 years) 238 64% 0.71 (0.59 - 0.83)

> 6 months - 1 year (0.9 years) 1,224 59% 0.61 (0.55 - 0.67)

> 1 - 2 years (1.5 years) 7,002 54% 0.55 (0.53 - 0.57)

> 2 years (2.6 years) 9,153 52% 0.51 (0.49 - 0.53)

P for trend 0.03

Time between completing identical questions on

the freq of any PA (avg time between the two) 6 months (0.3 years) 221 57% 0.67 (0.53 - 0.81)

> 6 months - 1 year (0.9 years) 1,171 53% 0.67 (0.61 - 0.73)

> 1 - 2 years (1.5 years) 6,044 48% 0.60 (0.58 - 0.62)

> 2 years (2.6 years) 5,312 47% 0.58 (0.56 - 0.60)

P for trend 0.05

Agreement of reported PA, by time between completing identical questionnaires


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Numberofwomen

Kappa (95% CI)with quadraticweighting

Agreement according to season of first responseversus repeat response, strenuous PA

Winter first response vs winter repeat response 1,110 0.52

Winter first response vs summer repeat response 665 0.54

Summer first response vs summer repeat response 1,118 0.57

Summer first response vs winter repeat response 1,052 0.51

Agreement according to season of first response

versus repeat response, any PA

Winter first response vs winter repeat response 708 0.57

Winter first response vs summer repeat response 509 0.58

Summer first response vs summer repeat response 830 0.63

Summer first response vs winter repeat response 908 0.58

Agreement of reported physical activity, by season of reporting


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Summary


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Simple questions on frequency of PA at baselineassociated with hours spend on specific activities &estimated excess MET hours ~3 years later

Weakest associations with housework

Agreement for identical questions on PA frequencyasked on two occasions decreased over time

Agreement similar for different seasons



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Methodologicalconsiderations


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Methodological considerations in PA

research

Combination of factors that may influence relationship

between PA and disease outcome

Past activity (over the life course)?

Present activity at baseline?

Changes in PA over follow-up time? Measurement error at baseline?


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Measurement error & PA assessment

Variability in answers when completing baseline questionnaire

Difficulty recalling past activity time periods, type Different interpretations housework, intensity

Social desirability bias

Random reporting errors

Real changes in PA over time

Lifestyle changes, retirement etc

Could be associated with morbidity reverse causality



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Influences of measurement error

Measurement errors likely to result in attenuation of estimatesof association between baseline PA and disease risk

Degree of attenuation depends on:

Assessment instrument

Participant characteristics

Intensive assessment may sources of error but oftenimpractical, expensive & alter natural behaviour



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Possible Approaches

Correct for regression dilution using objective measurements

Assess associations between PA at baseline and diseaseoutcome at follow-up split according to discrete time bands offollow-up

Report findings so readers may make their own conclusions



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Acknowledgements Million Women Study steering committee, co-ordinating centre staff, and

participants

Supported by Cancer Research UK and the Medical Research Council



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QUESTIONS?


Documents

Armstrong 2011 Methodology Seminar