Tracking Change Over Time Ensuring Comparability

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  • 1.Tracking Change Over Time: Ensuring Comparability Kinnon Scott DECPI More Frequent, More Timely and More Comparable Data for Better Results, PREM Week, April 20, 2011
  • 2.The consequences of not focusing on comparability Misallocation of resources
  • 3.Asset Indices: Poorest Quintile Overlap Source: Filmer and Scott, “Assessing Asset Indices” Demographics, forthcoming.
  • 4.The consequences of not focusing on comparability Misallocation of resources Loss of Credibility Effort to move to empirically based policy making Undermines all data (whole survey or NSO)
  • 5.Comparability Across countries Income vs. consumption PPPs Education levels Within country at one point in time Spatial cost of living adjustments Seasonality (Afghan for example) Within country over time
  • 6.It’s not rocket science Ask the same question Verbatim Categories Change with the changing world Reference periods Matters in consumption: collapsing, memory, etc. (Deaton and Grosh, 2000 for overview) Same time in the year- “Monga” Bangladesh Fixed reference period in moving survey: Uzbek education Respondent Random adult lack of knowledge (Cull and Scott, 2010; Bardasi et al, 2010) Head of hhlds attitude Aggregation More aggregation, lower level, memory issue
  • 7. Use verbatim questions
  • 8.CWIQ 2003 DHS 2003 CENSUS 2000 GLSS 1998 Measuring access to improved water sources in Ghana Use questions from previous surveys Examples taken from ADP, Neil Fantom, DECDG
  • 9.Affects the trends in indicators: Nigeria
  • 10.Uzbekistan-Reference Periods
  • 11.Field Work Interviewers, supervisors, data entry staff (and tools) all affect data collection Quality control Training 2-3 days versus 2-3 weeks Supervision Administrative vs substantive Data entry Ex Post Concurrent data entry (Glewwe and Dang, 2008) CAPI (SERPro, 2003; Caeyers, Chalmers and De Weerdt, 2010)
  • 12.Peru 2001-2004 Poverty numbers questioned Did an in-depth review of method of Questionnaire design Unit non-response Item non-response Imputations Non-sampling errors One of the key issue was decline in supervision and data quality controls in the field Changes in survey quality changed poverty levels!
  • 13.How to improve questions? Add new questions without dropping old Overlap with new versions-Income Colombia Experiment with new questions in parallel Within existing survey (Brazil POF) At pilot phase (Niger) Ex post (Malawi)
  • 14.Summary Comparability needs to be major focus Can be affected by all stages of the survey (questionnaire design through field work through imputations for non-response) Test all changes and overlap series Check for comparability when using existing data sets