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Immobility measured by transport surveys, evolution of the questionnaire from 1994 to 2008

Immobility measured by transport surveys, evolution of the questionnaire from 1994 to 2008. European conference on quality in official statistics Rome, ISTAT, 8-11 / 07 / 2008. Overview. Immobility in transport surveys, introduction Survey themes and definition of immobility

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Immobility measured by transport surveys, evolution of the questionnaire from 1994 to 2008

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  1. Immobility measured by transport surveys, evolution of the questionnaire from 1994 to 2008 European conference on quality in official statistics Rome, ISTAT, 8-11 / 07 / 2008

  2. Overview • Immobility in transport surveys, introduction • Survey themes and definition of immobility • Critics concerning the indicator’s quality • Accuracy, consistency, and relevance to improve • Changes in the 2008 questionnaire • Immobility during a week with sliding observation day • First attempt to compare 1994 data and 2008 partial data • Methods, results by age- and activity-type-groups • New indicators of immobility on a weekly basis • Number of “mobile days” per week, alternate immobility rate • Conclusions

  3. Introduction: the French national travel household survey • Main themes of “Enquête nationale sur les transports et les déplacements” • Socio-demographics • Equipment at disposal for transportation • Vehicles and licenses • Public transport pass • Parking facilities • Travel behaviour • Regular trips from home to work / school (most household members) • Daily mobility on a reference day (one selected member “kish”) • Long distance mobility the last three months (one selected member “kish”) • Weekly diary for trips made with one selected vehicle • One-year survey (April 2007 to April 2008), 18.000 households.

  4. Immobility in transport surveys, definition • No trip made on the closest weekday before the visit, i.e. the “reference weekday” • In 1994, 16% of the individuals were immobile on the reference weekday, because: • No need to go out : 73% • Temporary physical incapacity : 10% • Permanent physical incapacity : 6% • Need to stay at home : 5% (somebody ill at home, work to do) • Other : 6%

  5. Critics concerning the indicator’s quality • Accuracy: 2% of the 1994 sample is suspected of laziness or “soft refusal” • No trips declared on the reference weekday, Saturday, and Sunday because “no need to go out”, three times. • Consistency: discrepancies with Time-Use surveys (TUS) • Comparisons made on French, Belgian, and British data show large discrepancies: according to TUS, about 8% of the individuals stay at the same place during a whole weekday, according to NPTS, between 17 to 25%; though: • Data on the place of activity in TUS are not beyond reproach; • Belgian and British methodologies are based on self administrated paper questionnaire (Be) or diary (UK). • Relevance: one weekday is not enough • Insufficient information on people who seldom go out of home

  6. Changes in the 2008 questionnaire • In 1994, immobility is derived from one-day observations • Did you make trips between 4 that day and 4, the day after? yes/no • In 2008, immobility is observed on a sliding observation weekday defined by a series of questions: Last week, are there days when you have not been out ? 1)yesterday (the day, e.g. Monday) yes/no 2)the day before (the day, e.g. Sunday) yes/no 3) three days ago (the day, e.g. Saturday) yes/no … 7) seven days ago (the day, e.g. Tuesday) yes/no • The sliding observation weekday is the closest weekday when the respondent was mobile. Immobility, except if it was during the whole week, does not reduce the time of interview anymore. • Daily mobility is collected for 95% of the individuals • Weekly mobility profile now available for all individuals

  7. First attempt to compare 1994 and 2008 data • No correction for non response on 2008 partial data • Time period reduced to 10 months, March and April still missing for 2008 • Comparison on specific groups: • Age-groups by day of the week • 6-14 • 15-64 • 65-84 • Activity groups (15-64) • Students • Unemployed • At home • Retired • Employed working at home • Employed working at various places • Employed working on a fix place (Females or Males) • Scholars (6-14) during school or holidays periods

  8. Results: + 1994 immobility rate 2008 immobility rate 95% confidence interval With filter on questionable immobility in 1994

  9. Results: Students(>15) Stdnt Not working (<65) Retir: Retirement (<65) Not_W: Not economically active at work (<65) Unemp: Unemployed Children (6-14) Ch_sc: school period Ch_ho: holyday period Economically active at work (<65) W_swp: in several workplace Whome: at home W1wpM: in one workplace (males) W1wpF: in one workplace (females) + 1994 immobility rate 2008 immobility rate 95% confidence interval With filter on questionable immobility in 1994

  10. New indicators on a weekly basis • Are the mobile persons on the reference weekday always mobile during the week?

  11. Alternate immobility rate • Two ways to measure the rate of immobility on each weekday: the ranks do not change but difference can be significant. On average, a difference of almost 0.4 point. Pros : smaller standard error, stable indicator (last 4 days to last 7 days) Cons : possible memory effect (less immobility on remote weekdays)

  12. Conclusion • Accuracy and Consistency • “Soft refusal” seems, at least partly, controlled by the filter on three day-immobility without motive • 1994 filtered data seem consistent with 2008 partial data • Lower immobility rate in 2008 for elderly persons who are on average younger, wealthier, and in better shape than in 1994 • Higher immobility rate in 2008 for working persons because of more part-time work and more holydays • A new issue: discrepancy between the two possible estimators of immobility rate of almost 0.4 point. • Relevance • Weekly mobility profile is interesting to consider and follow over time

  13. Thank you jean-paul.hubert@inrets.fr sophie.roux@inrets.fr INSEE F340 18 Boulevard A. Pinard 75675 Paris cedex 14 France

  14. Appendix: Graphs taking into account the 2% of questionable immobile individuals

  15. + 1994 immobility rate 2008 immobility rate 95% confidence interval Without filter on questionable immobility in 1994

  16. Students(>15) Stdnt Not working (<65) Retir: Retirement (<65) Not_W: Not economically active at work (<65) Unemp: Unemployed Children (6-14) Ch_sc: school period Ch_ho: holyday period Economically active at work (<65) W_swp: in several workplace Whome: at home W1wpM: in one workplace (males) W1wpF: in one workplace (females) + 1994 immobility rate 2008 immobility rate 95% confidence interval Without filter on questionable immobility in 1994

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