BDI, CDI, MRI and BAS: computing the indices without inventing a universal convention.
Evidence status
What was reproduced, and what it does not prove.
The versioned specification and the educational fixture were verified. The Python run reproduces BDI 80 and CDI 120, and rejects a null population or a share out of range. MRI and BAS remain deliberately unavailable without a convention.
- Technical specification of BDI and CDI, specification in French (opens in a new tab)
v1, 31 August 2026 · CC BY 4.0 · specification in French · Method document written by marketing-mix.net. The figures are illustrative: they are not market measurements.
Key distinctions
Three conditions before calculating.
A relative base of 100
An index of 120 means 20% above the defined base, not absolute performance or causation.
Strictly comparable units
Sales, population, period and scope must be aligned. Mixing value, volume or areas invalidates the ratio.
MRI and BAS by local agreement
These acronyms can cover several methods. The exact formula and its source are part of the result, not of an appendix.
Method
Computing and interpreting without over-promising
- 01Define market, brand and category
Record area, period, unit and source; the population share uses the same scope as the sales.
- 02Compute the relative shares
BDI = brand sales share / population share × 100. CDI = category sales share / population share × 100.
- 03Read the two indices together
BDI and CDI describe a configuration. On their own they do not say whether the gap comes from distribution, price, demand or competition.
- 04Document the proprietary indices
For MRI or BAS, record formula, weightings, data, treatment of missing values, base, frequency and owner.
BDI and CDI calculator, MRI and BAS register
The calculator uses shares expressed in the same unit. MRI and BAS remain unavailable until their convention is documented.
Descriptive result: it is neither an allocation recommendation nor causal proof.
Formula, base, period, source and interpretation.
Dimensions, weightings, missing values and thresholds.
An under-developed brand in an over-developed category
Illustrative example: an area represents 10% of the population, 8% of brand sales and 12% of category sales.
BDI = 8 / 10 × 100 = 80. CDI = 12 / 10 × 100 = 120.
The contrast warrants an investigation into availability, preference, price and competition. It proves neither a causal potential nor an optimal allocation.
Acceptance conditions
What must be true to act.
- 01
Use the same area, period and unit for the numerator and the denominator.
- 02
Show the source shares alongside the index so that the calculation is reproducible.
- 03
Treat missing data as unavailable, never as zero.
- 04
Reject an MRI or BAS without an explicit formula, base, source and weighting rule.
Limits
What this analysis does not prove.
- BDI and CDI are descriptive and sensitive to the definition of the market and the population.
- A base of 100 is neither a universal objective nor an automatic investment threshold.
- MRI and BAS can be company or supplier conventions that are not comparable with each other.
- These indices do not replace incremental analysis or financial brand measurement.
References