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Máximo Ramírez edited this page Nov 8, 2017 · 3 revisions

About this documentation

This documentation aims to complete and complement the original documentation provided by MACEPA in the Wiki of the GitHub project repository. Therefore, some chunks of this document are directly copied and pasted in here.

About EpiSample

According the EpiSample documentation posted on GitHub by MACEPA (Tim McDonald):

EpiSample is a new Android application that builds off of ODK 2.0 tools and offers additional census, sampling, and survey capabilities that facilitate the implementation of population-based epidemiological surveys. EpiSample features are largely based on GPS2, a Windows Mobile application that was designed and developed by Anatoly Frolov to run on personal digital assistants (PDAs).

Features

EpiSample provides mainly with the following features:

F1: Census

  • Allows an enumerator to easily select a specific geographic region from a list of hundreds or even thousands of place names by traversing through a hierarchical list that starts from the highest geographic level (for example, Province) to the lowest level (for example, "EA" or Enumeration Area).
  • Efficiently capture GPS coordinates of points (such as households), the name of the head of the household and a comment.
  • Send out multiple teams with multiple devices to conduct a census and aggregate all of the census data onto one device (such as a team leader device) for sampling, without the need for a laptop, Internet or cables.
  • Capture points of interest to aid navigation and exclude these points from the sampling frame.

F2: Sampling

  • Apply a random sampling algorithm to a listing of points to select:
    • Main points: These are the primary points (typically households) to survey.
    • Additional Points: These are the oversampled points (if needed).
    • Alternate Points: These are the extra points which can be used in the event a household from the main points or additional points list is unavailable or unsurveyable.
  • Lock-down the number of points to sample via password protected configuration, or let the team lead choose how many to sample while in the field.
  • Record the date/time of when the sample happened and the total number of points included in the sampling frame.

Random sampling algorithm used by EpiSample

// Valid points are those in which the accuracy is better than the defined
// threshold (See Task 4: Configure Collect module from the How to install page)
Array points = getAllValidPoints();

// Assing random values to each census point and sort by these values
assignRandomValues(points);
sortPoints(points);

// Compute selection parameters
int pointsToSelect = mainPoints + additionalPoints + alternatePoints;
int selectionSize = 0;
if (points.size() > pointsToSelect)
  selectionSize = pointsToSelect;
else
  selectionSize = points.size();

// Make points selection
for (int i = 0; i < selectionSize; i++) {
  if (i < mainPoints)
    points[i].setSelectedAs(MAIN_POINT);
  else if (i >= mainPoints && i < mainPoints + additionalPoints)
    points[i].setSelectedAs(ADDITIONAL_POINT);
  else if (i >= mainPoints + additionalPoints && i < pointsToSelect)
    points[i].setSelectedAs(ALTERNATE_POINT);
}

Note: This is a global random selection strategy. I.e. geographical dimension is not considered for sampling. Therefore, we cannot assume a uniform distribution of selected households across clusters. Sampling may result in clusters without any selected household.

F3: Surveying

  • Survey sampled points that were previously captured from the Collect module.
  • Survey points that were imported from a CSV file.
  • Filter and/or sort points in various combinations based on the type of point, distance from the device, time of data entry, interviewer name, Android device identification number, or enumeration area where the point is located.
  • Navigate to a household using a built-in compass that shows the current heading, the bearing (direction) to the household and the distance to the household from the current position. -Once at the household, bring up a survey and conduct it directly in ODK Survey.
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