Guideline: Rating Algorithm
A Cross sectional view of OMM with questions derived from practices is the base for the rating algorithm. In principle: a maturity level (ML) of OMM is achieved when all TWEs assigned to that maturity level are fully implemented; a TWE is fulfilled when all of its goals are fully implemented; and; a goal is fulfilled when all of its practices are fully implemented.
Main Description

In an assessment ratings are assigned only to the practices which are associated with a maturity level (which are contained in the TWEs of that ML). That means, the maturity level is only indirectly based on the fulfilment of all TWEs and goals. (For details see below: Rating of Practices) Each practice gets a rating from following scale: 

3 - (fully implemented);

2 - (partially implemented);

1 - (not implemented);

0 – (not applicable).

These are the points achieved by a practice based on the evidence (e.g. LookFors, Metrics data, documents) presented to the assessment team. This scale (0 to 3) defines the maximum points that can be reached by a practice. As explained above, the points earned for each practice directly determine the maturity level. A maturity level is reached when the total rating of at least 90% for the practices in that maturity level is achieved.

Rating of Practices

The basic idea is to check the fulfilment of a practice with LookFors or Questions. Both are optional. They merely indicate what could be found as implementation of the practice.
Each practice can have only a single rating based on the perceived fulfilment of each of the Questions/LookFors. By perceived is meant that the LookFors are not rated but if ALL LookFors in a practice are completely fulfilled, then the practice is likely to be rated 3. Similarly, partial achievement of the LookFors earns a rating of 2 for the practice. There is no real rating of the LookFors. It is important to bear in mind that LookFors are only indicators for required contents of the practice and they are not always an exhaustive list of requirements for the practice.
A Question/LookFor can also be rated as not applicable. But normally there should be very few of these, because the OMM includes only the essential practices as mandatory elements.

Metrics help to measure the implementation of the practices.The thresholds of the metrics (especially from the automatically calculated ones) are used to classify to what extent the practice is implemented. For the rating of the practice the assessor has to look at the evidence for the questions/LookFors are and has to decide about the final rating for the practice.
As a result each practice gets a rating of 3, 2, 1 or 0. The rating results for the practices are now the basis for further rating. A special treatment for the practices which get the rating “not applicable” (0) is necessary.

Rating algorithm for Goals:

R(Gj): 1. build Average (Pi)

2. For the exact rating truncate result but also communicate the exact result to provide information about the degree of fulfilment.

Rating algorithm for Trustworthy Elements:

R(TWEj):       1. build Average (Pi)

2. For the exact rating truncate result but also provide the exact result to provide information about the degree of fulfilment

Rating algorithm R for Maturity Level L

R(L): Sum(Pi) / maxSum(Pi)

1. maxSum(Pi) are the maximum points reachable through the mandatory practices assigned to that level.
2. Sum(Pi) are the points reached for that level. In a first step only the points from mandatory practices assigned to that level are calculated. Eventually Pi‘s from recommended practices and Pi’s from higher levels could be honoured (see below: How to find relevant Pi‘s for the calculation of a OMM maturity level:

OMM rating (overall rating)

Two types of ratings are possible: (1) Calculation of the reached OMM maturity level and (2) Calculation of the fulfilment of the individual TWEs and goals.

Calculation of OMM maturity levels: R(L)= Σ(Pi) / max Σ(Pi)
• OMM Level reached : 90% ≤ R(L)
• OMM Level not reached: R(L) < 90%

How to find relevant Pi‘s for the calculation of a OMM maturity level:
1. Calculate R(L) only with mandatory practices assigned to the level

2. If R(L) ≥ 80%, bonus points can be awarded

Bonus = 0,5 x (recommended practices (from ML) +
+ mandatory practices (from ML+1) +
+ mandatory practices (from ML+2)

3. Recalculated Level: R(L) = (Bonus + Σ(Pi)) / max Σ(Pi)
Higher levels are only calculated, when lower levels are reached.