7. Define SRS grid layout

Overview

In this step, the SRS (systematic random sampling) grid size defines how close your counting frames are to each other.

Smaller grid: You visit more sites within the traced contour, and count more cells or other objects.
Larger grid: You count objects at fewer sites, but you may increase your coefficient of error and obtain a less-precise estimate.

See Designing a Pilot Study for recommendations on determining the grid size. For the pilot study, we recommend setting the grid size based on 10 approximate sampling sites as a starting point.

Also see Determining Sampling Precision.

Procedure

Define SRS grid layout

Choose one of the following ways to define the SRS grid layout:

Manually enter the grid size:
1. Type in values (µm) for X and Y grid spacing.
2. Click Display Changes.
Enter a percentage of the region of interest that you want to sample:
1. Type the percent to sample in the Percentage box.
2. Click Display Changes
Determine grid size based on number of sampling sites:
1. Enter the desired number of sites in the Approximate Sites box.
2. Click Estimate Grid Size.
  
  This option is ideal if you don’t know your desired X and Y grid spacing. For instance, if you want to count a mean of 10 sites based on the current representative section, set the grid size to include approximately 10 counting frames in the region of interest.

Grid size and counting frame size remain consistent throughout all of the sections for a given region of interest. The number of sites, however, may change because the grid is applied randomly every time you start a new probe run. Click Display Changes or Estimate Grid Size repeatedly to see how the grid is applied differently every time.

Round to increments of: We recommend that you check the box to round the values to 1 micron or larger to make it easier to remember and document as needed.

Undo my changes: Click to remove your input for this step and revert to the default values.