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Task of the Dutch National Travel Survey (OVG)

Task of the Dutch National Travel Survey (OVG). “To establish the mobility pattern of (specific groups of) the Dutch population by point of departure and destination, period of mobility, mode of transport and purpose of the journey”. About OVG.

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Task of the Dutch National Travel Survey (OVG)

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  1. Task of the Dutch National Travel Survey (OVG) “To establish the mobility pattern of (specific groups of) the Dutch population by point of departure and destination, period of mobility, mode of transport and purpose of the journey”.

  2. About OVG • Target population: resident population of the Netherlands • Sample frame 1978-1998: Geographic Basic file, Municipal • Sample frame 1999-2003: Basic Administration • Every household has an even chance of being selected • Collecting data on actual behaviour • Excluded mobility during holidays • No foreign mobility

  3. household person person person trip trip trip Datastructure OVG size composition vehicles adress sex age income education occupation vehicles destination purpose modes distance time mode distance stage stage

  4. Some figures about OVG • From 1978 - 2003: • 26 years • 9,496 days • 3 different observation methods • 700,000 households • 1,500,000 persons • 5,000,000 trips

  5. Mobility figures 2003 Trips per person per day: 3.15

  6. History OVG 1978: start face-to-face, trips during period of 2/3 days 1985: new design (first redesign) mixed method (CATI & mail-out/mail-back), trips during one day 1995: expansion (financing by AVV) 6X sample and extra questions 1999: New OVG (second redesign)

  7. Procedures • New OVG 1999-2003 Old OVG 1985-1998 Old OVG 1978-1984 • Introduction letter Introduction letter Introduction letter • Questionnaires (mail) Telephone-interview First interviewer visit • Response motivation (tel.) Diaries (mail) Diaries (mail) • Recalls (tel. and mail) Recalls (mail) Second interview visit • Follow-up surveys (tel.)

  8. Problems OVG • declining telephonic accessibility • increasing unwillingness to participate • doubts about representativeness and comparability • design was not flexible due to claim of continuity and comparability

  9. Response rates OVG 1985 - 1998 100% 90% 80% Phone number 70% 60% 50% Response CATI Response 40% Response diaries 30% Complete 20% households 10% 0% 85 86 87 88 89 90 91 92 93 94 95 96 97 98

  10. New Design • Respondent-friendly design • Mixed modeBasic Survey • mail-out/mail-back (household, persons) • motivation by telephone • ‘Satellite’ surveys (follow-up surveys) • to obtain additional data for specific subgroups or research topics • mail-out/mail-back or telephone interview • Project organisation

  11. New Design Persons under 6 year (T) answer- problems (T) BASIC SURVEY (all household members older than 6 years) Satellite (T) Public Transport (T)

  12. Scheme New OVG Sample from Basic Admin. Assigninterview day no tel.nr: Basic Adm (name) Linking telephone numbers Introduction letter postal interview: same procedure as households with telephone questionnaires, letter, extra info Motivations by telephone Questionn. not back in 1 wk Questionnaires back in 1 week Visual-check Children < 6 years Follow-up Public transport answer problems 2e/3e tel. motivation/ reminder-call Follow-up children Follow-up interview. non-response Data-entry Analyzing data Publication (Statline)

  13. Response rates New OVG

  14. Population of the Netherlands Sample frame Sample OVG Sample N(ew)OVG Telephone Respondents Respondents Notelephone Non-Respondents Non-Respondents

  15. Mobility figures parallel run NOVG 1998

  16. Correction OVG 1985 - 1998 • NOVG results in higher response rates but records significantly lower mobility • Analysis to correct OVG data comprises three steps • qualitative analysis of differences • quantifying this differences • presenting quantitative method to correct non-response bias in OVG-data

  17. Imputations and corrections • Select year under review • Day of completion • Couple with municipal-registers • Impute age, gender unknown • Incorporate remarks data entry • Check relations between age and respondent • Car characteristics: year of construction and fuel • Possession of: bicycle, moped, driving licence • Delete trips with lorries • Impute frequent trips (made by postman, doctors) • Check and imputation of: distance and travelling • Select non-mobile persons and non-respondents • Impute public transport data folluw-up survey

  18. Correction of the break in the series • Implement the response probability model and calculate correction weights based on the New OVG since may 1998. • Use correction weights to adapt the original respons probabilities of the older years of the OVG (1985-1998). • Apply the usual (linear) weighting model to regain consistency with the population numbers. • Implement table correction on basis of (trip) purpose and main mode of transport

  19. Table correction factors • Add recreative purposes: - Touring/walking- Recreation/sport • 4 table correction factors: - number of trips- (trip) travel distance- (trip) travelling- (stage) distance

  20. Mobility figures 1998 - 1999 Distance pppd (before correction)

  21. Mobility figures 1998 - 1999 Trips pppd (before correction)

  22. Mobility figures 1998 - 1999 Trips pppd 12 yrs plus (after rough correction)

  23. Mobility figures 1998 - 1999 Distance pppd (after rough correction)

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