Stereology techniques
Only a fraction of the material advances to the next step of the sampling procedure. In a cascade design the material being sampled is repeatedly subdivided. A boundary can be formed by the perimeter of a profile resulting when a plane intersects a 3D object. A boundary is the outer edge of a 2D area. Some common sources of bias are 1) limitations of technique (inadequate contrast, positive section thickness, overlap and truncation effects etc.) 2) statistical bias arising from the sampling design, 3) geometrical bias arising from discrepancies between a stereological model and reality. Bias causes the mean of the estimated values to deviate from the true value. Often abbreviated as asf.Ī statistical sampling or measurement error caused by systematically favoring some outcomes over others. The ratio of the counting frame area to the area formed by the fractionator sampling grid. The forbidden line method is the other method of particle counting. Note: there are at least two methods of deciding if an object is to be counted by a counting frame. It may be problematic to apply the associated point rule in some cases because of the difficulty in deciding whether the associated point falls inside or outside the sampling volume in marginal cases. If this unique point falls within the counting frame, then the object is counted in that counting frame. Whatever type of point is used, it is critical that this point can be uniquely identified for all of the objects to be counted. For example, this point may be the nucleus, center of mass, the leftmost point or the topmost point. This unique point is then associated with the object. In this method, a particle is reduced to a unique point. Care must be taken when probes cross-artificial edges.Ī method of deciding if an object is to be counted by a counting frame. Cutting objects such as organs produces artificial edges.
The effect is to reduce the overall variance. The idea is to tie together things such that an increase in variance in one place reduces the variance in another. Having properties that differ according to the direction of measurement.Ī method reducing the variance. This is a biased formula and should be avoided.Īccuracy is a measure of how close an estimate or measurement is to the actual or true value. It attempts to correct for over counting by adjusting the count by a factor based on the section thickness and the average height of the particles being counted. This is the most commonly used counting correction formula.