Wastewatch

Tool Instructions

Instructions

Welcome to Wastewatch – a simulation-based tool for evaluating statistical methods for detecting changes in wastewater data. This tool is designed to help you understand how different surveillance methods (such as Shewhart, EWMA, and MC-EWMA charts) perform in detecting significant changes that may be associated with epidemics.

How to Use Wastewatch

  1. Baseline Data: Choose the behavior type for your baseline data.
    • Stable: Data generated using a fixed mean and standard deviation. You can choose between a normal or lognormal distribution.
    • Trending: Data with a linear trend plus noise. Provide a starting value, slope, and noise level.
    • Periodic: Data that fluctuates periodically. Provide the mean, amplitude, period, and noise level.
  2. Inducing a Change: Optionally, you can induce a change (simulating an epidemic) in the data.
    • Step Change: The data’s mean is multiplied by a given factor starting on a specified day.
    • Trending Change: A new trend (with its own slope) is added for a specified duration.
  3. Surveillance Method: Choose the analysis method.
    • Shewhart: Monitors individual data points using control limits.
    • EWMA: Uses an Exponentially Weighted Moving Average, which incorporates a lambda value to weight recent observations.
    • MC-EWMA: A variation of EWMA where the center line is updated differently. You can also choose to optimize lambda here.
    For EWMA and MC-EWMA, you have the option to enter a lambda value manually or use the "optimized" setting, which automatically finds the lambda value that minimizes the squared residual error over the baseline period.
  4. Simulation Parameters: Specify the number of days for the baseline data, the number of replications, and the sigma multiplier (used to set the control limits).
  5. Important Note: The change day must always be greater than the number of days used for baseline data.
  6. Analyze: Click the "Analyze" button to run the simulation. The results page will display control charts for several replications, a histogram of run lengths, and key performance metrics.
  7. Reanalyze: Use the reanalysis form to adjust parameters or change the analysis method without re-entering all of the baseline settings.

Use the navigation links above to return to the main simulation page or to revisit these instructions.