Shape Factor

See Area Fraction Fractionator probe, Cavalieri Estimator

The shape factor is the perimeter of the contour around the area of interest divided by the square root of the area.

It is a component of the formula used to calculate the coefficient of error (Coefficients of Error).

Stereo Investigator does not calculate a shape factor; instead, it defaults to the value 4.0.

 

If you determine the shape factor of the areas you are estimating by measuring or estimating the mean area and boundary for your regions, you can modify the shape factor constant used in the CE equation to see the impact on the CE calculation.

Modifying the shape factor does not change the estimated area or volume; it only alters the CE of the estimated area or volume.

How do I determine a shape factor?

Choose a shape factor on the basis of how the region compares to other shapes:

  1. Click Move>Where Is to get an aerial view of the region of interest.
  2. Click Probes>Stereology results>Probe run list.
  3. Click the View Results button. The Sampling Results dialog box opens.
  4. Click the Edit Shape Factor button. The Shape Factor dialog box opens . After changing the shape factor, the calculations that depend upon it are automatically updated.

OR

Calculate and enter the average shape factor.

  • Define the boundary then use the estimate of areas.
  • If you have contours traced, you can find the Shape Factor for each contour used in the Contour Measurements window.

 

The Contour Measurements window also contains area information for the contour. Be aware that this information is calculated assuming that the tracing is accurate to the nearest pixel. Use of the Cavalieri method is required to obtain an unbiased estimate.