Plasma (physics) potential in the space between charged particles, independent of how it can be measured, is called the "plasma potential", or the "space potential". If an electrode is inserted into a plasma, its potential will generally lie considerably below the plasma potential due to what is termed a Debye sheath. The good electrical conductivity of plasmas makes their electric fields very small. This results in the important concept of "quasineutrality", which says the density of negative charges is approximately equal to the density of positive charges over large volumes of the plasma (formula_6), but on the scale of the Debye length
Positive and negative predictive values the same as the prevalence in the control group used to establish the negative predictive value, then the two are numerically equal. The following diagram illustrates how the "positive predictive value", negative predictive value, sensitivity, and specificity are related. Note that the positive and negative predictive values can only be estimated using data from a cross-sectional study or other population-based study in which valid prevalence estimates may be obtained. In contrast, the sensitivity and specificity can be estimated from case-control studies. Suppose the fecal occult blood (FOB) screen test is used in 2030 people to look for bowel cancer: The