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Using a PDA with GPS to choose a sample and conduct a survey.

Using a PDA with GPS to choose a sample and conduct a survey. . Statistical and Spatial Considerations Allen Hightower. First, an Introduction. 32 st Year at CDC 17 h Year working at Kenya Field station (3 year resident) Biostatistician by training and experience Longitudinal/Survival

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Using a PDA with GPS to choose a sample and conduct a survey.

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  1. Using a PDA with GPS to choose a sample and conduct a survey. Statistical and Spatial Considerations Allen Hightower RBM-MERG Malaria Indicator Training Workshop, 9th-12th September 2008, Lusaka, Zambia

  2. First, an Introduction • 32st Year at CDC • 17h Year working at Kenya Field station (3 year resident) • Biostatistician by training and experience • Longitudinal/Survival • Vaccine Studies • Statistician for Am J Trop Med • GIS/GPS mapping/spatial analyses since 1990. RBM-MERG Malaria Indicator Training Workshop, 9th-12th September 2008, Lusaka, Zambia

  3. More to this than technology!!! • This is a system that uses technology. • Software development and testing. • Training, training. • Stay in touch with the data collectors in the field regularly. RBM-MERG Malaria Indicator Training Workshop, 9th-12th September 2008, Lusaka, Zambia

  4. Training!!! • Can train people to use a lousy system • Poor training can ruin a perfect system • Learn how to solve common problems • Tip sheets/manuals • Training schedules/exercises • Stay in touch with the data collectors in the field regularly. RBM-MERG Malaria Indicator Training Workshop, 9th-12th September 2008, Lusaka, Zambia

  5. Software Development tools • We use MS Visual Studio 2005/Visual Basic for most of our systems • SQL server (can have Access front end) • SQL mobile on PDAs • “Same” software tools for pcs, pdas, smart phones. • We do use other products ! • PDA: Visual CE (www.syware.com) RBM-MERG Malaria Indicator Training Workshop, 9th-12th September 2008, Lusaka, Zambia

  6. PDA data collection: How safe? Data saved field-by-field • Battery Loss – non-issue. • Memory is nonvolatile like a digitall camera. • Battery life >>16 hrs • Better than laptop/tablet computers • Big screens, HDs use power! • No moving parts (ie, better than a laptop) • Encryption/PW at OS level • PDAs we use are very, very sturdy. • Have never had one stolen/lost. RBM-MERG Malaria Indicator Training Workshop, 9th-12th September 2008, Lusaka, Zambia

  7. PDA data collection: Can Paper do this? • Live skip patterns – less training • Only see the right questions. • QC at Data Collection point • Autoword completion: less typing • Turn off unneeded features (games/buttons) • Know where interviewer is/should be • Know when the interview started/stopped • Very, very rapid data availibility RBM-MERG Malaria Indicator Training Workshop, 9th-12th September 2008, Lusaka, Zambia

  8. Concept of PDA-GPS system • Interview teams take nothing more than PDAs with attached GPS units into a cluster • Map HHs in the cluster • Choose a statistically valid sample • Conduct Software Guided Interview w/PDA • Data Rapidly Available for Reporting/Spatial Analyses RBM-MERG Malaria Indicator Training Workshop, 9th-12th September 2008, Lusaka, Zambia

  9. PDA-GPS mapping system • Simple, fast • Most clusters mapped in 4 hrs or less • Village Name (auto carry) • HH number (auto increment) • Comment (e.g., the house in the middle, family name) • GPS gets you close, Comment provides final ID info • Allows Multiple mappers RBM-MERG Malaria Indicator Training Workshop, 9th-12th September 2008, Lusaka, Zambia

  10. GPS Survey Program:GPS readings • Program checks the CF-GPS unit for a valid reading • Gives color coded GPS validity • Green – good precision • Yellow – marginal • Red – poor • Random number assigned to HH when data are saved. RBM-MERG Malaria Indicator Training Workshop, 9th-12th September 2008, Lusaka, Zambia

  11. RBM-MERG Malaria Indicator Training Workshop, 9th-12th September 2008, Lusaka, Zambia

  12. Sampling Design • It is your decision! • The system only affects how households or compounds are sampled within a cluster. RBM-MERG Malaria Indicator Training Workshop, 9th-12th September 2008, Lusaka, Zambia

  13. GPS Survey-Sampling: • You tell the PDA program : • How many HHs to sample from the EA. • How many alternates HH’s? • SRS or Cluster Sample • Parameters set up in XML file • You get: • a random sample where each HH has a known probablity of selection. • A File of the GPS data for all mapped HH’s and features of interest • Denotes which HH’s are in the sample RBM-MERG Malaria Indicator Training Workshop, 9th-12th September 2008, Lusaka, Zambia

  14. GPS Navigation Software • Guides the interviewer back the sample HH • List of HH ID’s with distance and compass direction /pointer • Also a map of HHs • Can mark HH off list • Can divide a list RBM-MERG Malaria Indicator Training Workshop, 9th-12th September 2008, Lusaka, Zambia

  15. GPS Navigation Software • List of HH ID’s with distance and compass direction/pointer • Can mark HH off list • Can divide a list to allow multiple interviewers to split work. RBM-MERG Malaria Indicator Training Workshop, 9th-12th September 2008, Lusaka, Zambia

  16. GPS Navigation Software • Also a map of HHs • Can show HH ID info RBM-MERG Malaria Indicator Training Workshop, 9th-12th September 2008, Lusaka, Zambia

  17. Advantages of GPS-based Simple Random Sample • Gold Standard Approach • SRS – better precision than other approaches. • Unbiased (accurate) • Any HH in village can be a part of sample • You know the probability of selection for a HH. • IE, a probability sample. • Spatial Analyses RBM-MERG Malaria Indicator Training Workshop, 9th-12th September 2008, Lusaka, Zambia

  18. Why is “Statistical Validity” Important? • For any survey, even those not using statistically valid methods, you can compute means, proportions, std errors. • However, to know the statistical distribution and compute confidence intervals for the means and proportions, you MUST use a random sampling process. • Or you must pretend that you used a random sampling process. RBM-MERG Malaria Indicator Training Workshop, 9th-12th September 2008, Lusaka, Zambia

  19. How much work to map cluster? • 4 hours to map the EA, typically • Some take 2 days! • 1 to 3 minutes between GPS readings (between HH’s) • Each interviewer mapped between 30 to 45 HH’s per EA RBM-MERG Malaria Indicator Training Workshop, 9th-12th September 2008, Lusaka, Zambia

  20. GPS can be used for quality control. Here we caught someone standing in one place. All GPS readings were within 60m. Sept 2005 Bad (Red): Green =remapping of village! RBM-MERG Malaria Indicator Training Workshop, 9th-12th September 2008, Lusaka, Zambia

  21. Can Produce a Map of HH’s in each EA,Showing which were in the Survey • Survey Program produces Database file with: • Lat/Lons for all HH’s in EA • Indicator for whether HH was included in sample • Lat/Lons for all other features of interest • Easily Imported into other GIS products RBM-MERG Malaria Indicator Training Workshop, 9th-12th September 2008, Lusaka, Zambia

  22. Not the first time this has been done! For All: Data Available within a week after survey • Togo: Jan – Feb 2005: 2500 HH in 2 week survey • Niger : Jan – Feb 2006: 2500 HH in 2 week survey • Mozambique : Jan – Feb 2006: 4500 HH in 2 week survey • Zambia: April 2006: 3000 HH in 2 week survey • Kenya: Oct 2006: 2000 HH Bednet Ownership Usage survey in 2 weeks. • Kenya: June/July 2007: 7200 HH Malaria Indicator Survey in 5 weeks. RBM-MERG Malaria Indicator Training Workshop, 9th-12th September 2008, Lusaka, Zambia

  23. Standardized data collection tools! • MIS’s in Zambia, Kenya, Ethiopia • Bednet Ownership/Usage surveys in a number of countries. • Comparable methods, systems • Extremely cost effective if systems and pdas are used multiple times. • Not sure it is worth it to do just once! RBM-MERG Malaria Indicator Training Workshop, 9th-12th September 2008, Lusaka, Zambia

  24. Thank you! RBM-MERG Malaria Indicator Training Workshop, 9th-12th September 2008, Lusaka, Zambia

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