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The percentage difference between the winning bid and the second-lowest valid bid is a low outlier.
See also: R058 - Winner close to submission deadline

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Methodology

For each contracting process, the difference is calculated as: 
(secondLowestValidBidAmount - winningBidAmount) / winningBidAmount
A contracting process is flagged if the difference is less than or equal to the lower fence of: 
Q1 - 1.5(IQR)
Where:
  • Q1 is the first quartile (25th percentile) of all differences
  • IQR is the interquartile range (Q3 - Q1)
  • This is a standard statistical method for detecting outliers
Both the winner and second-lowest bidder are also flagged.
Example:In 25% (Q₁) of contracting processes in Atlantis, the second-lowest valid bid is at most 5% greater than the winning bid. In 75% (Q₃) of contracting processes, it is at most 7% greater. This yields a lower fence of 2% (0.02).In a contracting process, CollusionCorp won with a bid of 100,000,andProcureManipulatelostwiththesecond−lowestbidof100,000, and ProcureManipulate lost with the second-lowest bid of 101,000. The difference is 1% (0.01). This is less than the lower fence of 2%, so the process is flagged.
Why is this a red flag?A colluding bidder can mimic competition by submitting a bid that is similar in price (but different in quality, for example) from its colluding partner. This creates the appearance of competition while ensuring the predetermined winner receives the contract.

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Output

The indicator returns different values depending on the entity: For contracting processes: The difference value as a decimal (e.g., 0.01 for 1%) For tenderers: Always 0.0 (to indicate they are flagged) If the --map command-line flag is set, the Maps key contains:
  • ocid_tenderer_r024: The flagged tenderers for each flagged OCID

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Configuration

All configuration is optional.
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threshold
float
Override the calculated lower fence with a fixed threshold. When set, the statistical calculation is bypassed.
[R024]
threshold = 0.05
This would flag any contracting process where the difference is ≤ 5%.
See also: no_price_comparison_procurement_methods and price_comparison_procurement_methods in global configuration for excluding certain procurement types from price-based indicators.

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Exclusions

A contracting process is excluded if:
  • An award’s status is pending or invalid
  • The winning bid is not the lowest bid (this indicator requires price-only award criteria)
  • There are multiple active awards (multiple winners) - see issue #14
  • A bid is submitted by multiple tenderers (joint ventures) - see issue #17
  • An award is made to multiple suppliers - see issue #17
Want to eliminate an exclusion? Please contribute to the linked GitHub issues.

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Assumptions

This indicator assumes that the tenderer of the winning bid didn’t submit another valid bid.

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Example Output

Input (OCDS JSONL with bids): 
{"ocid": "ocds-213czf-1", "awards": [{"status": "active", "suppliers": [{"id": "W"}], "value": {"amount": 100000}}], "bids": {"details": [{"tenderers": [{"id": "W"}], "value": {"amount": 100000}, "status": "valid"}, {"tenderers": [{"id": "L"}], "value": {"amount": 101000}, "status": "valid"}]}}
Command: 
ocdscardinal indicators --settings settings.ini --no-meta data.jsonl
Output: 
{"OCID":{"ocds-213czf-1":{"R024":0.01}},"Tenderer":{"W":{"R024":0.0},"L":{"R024":0.0}}}

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Implementation Details

From src/indicators/r024.rs:19-48: The indicator:
  1. During processing: Calculates the ratio for each contracting process and stores in second_lowest_bid_ratios
  2. During finalization:
    • Computes quartiles (Q1, Q3) and IQR from all ratios
    • Calculates lower fence using Tukey’s method
    • Flags processes where ratio ≤ lower fence
    • Also flags both the winner and second-lowest bidder
  3. Optimization: Skips flagging if Q1 ≤ 0 (would flag 75% of processes)
This is a relative indicator that requires sufficient data across multiple contracting processes to establish meaningful statistical thresholds. With small datasets, the lower fence may be unreliable.