Multiple of the median

In a MoM value is a unit that uses a measured value to an average in relationship. The MoM value describes so, how much higher or lower is a measured value with respect to an ideal value.

Origin of the term

The abbreviation " MoM " is derived from the term "multiple of the median " from. Translated, this means: " multiples of the median " or " multiple of the central value ." In average, the referring here, so it is the median or the median and not the mean.

Application

The MoM value can be used wherever a comparison of direct measurements leads to no useful result. This is particularly true of individual measured values ​​, which vary systematically in time.

Example of use

Will a pregnant woman compare their personal AFP lab value with an ideal value, it makes no sense to choose the average of a whole period as a reference, for example, the average AFP concentration 15 to 20 weeks gestation. If one forms the systematic upward slope of the AFP concentrations over this period from, it is clear that a comparison makes sense only for the particular stage of pregnancy in which the pregnant woman is. A woman in the 15th week compares its value so useful with the reference value of the 15th week of the adjacent figure: Cheating their AFP concentration in the 15th week exactly 22 IU / mL, then the MoM value would be at 1 ( the Simple of the median). At a concentration of AFP of 44 IU / ml of the MoM value at 2 ( two times the median), and at a concentration of AFP of 11 IU / ml would be lay the MoM value from 0.5 ( one-half the median ). In another pregnancy week intervals MoM values ​​for other concentrations. So would correspond approximately to the following 16 week 1 MoM a concentration of 28 IU / ml, 2 MoM one of 56 IU / ml and 0.5 MoM one of 14 IU / ml.

Applications

An emphasis on the use of MoM values ​​can be found in the field of prenatal diagnosis. In particular, when prenatal screening for chromosomal abnormalities and neural tube defects never direct measurements, but almost exclusively MoM values ​​or their logarithms are used in the risk calculation. The use of such mathematical MoM values ​​in this form of risk analysis is sound and described in detail in Palomaki and Haddow and at Reynolds and Penney.