Should percentage be banned from site data reporting? 5 reasons why you may agree

July 14, 2022
Percentages seem harmless enough, why would they need to be banned from site data reporting?

Percentages seem harmless enough, why would they need to be banned from site data reporting? After all, they're just another way to represent a relationship between two numbers.

But don't be fooled, percentages are actually a potentially dangerous and confusing way to express numerical relationships.

That's why we’re going to explore 5 reasons why you may want to consider banning the use of percentages for reporting…

It's relative, not absolute

Percentage in its simplest form is the rate or amount per one hundred.  However for site works where units are often different and rarely counted in hundreds it’s generally the expression of a proportion of the whole amount.  On this basis it is always relative and not an absolute amount.

This causes issues particularly where percentages are applied on a recurring or compound basis without knowledge of the original whole amount.

It's prone to errors

Rounding is common in calculating percentages which may compound to create material errors in reporting.  As percentage has no concept of timescale or absolute measurement it’s common for errors to occur when requesting figures to be reported in percentage as different teams use different relative measures and time periods.

It's hard to make comparison

To make accurate comparisons with any reporting data it’s critical that the same unit of measure is applied consistently.  When percentages are used it becomes extremely difficult to compare data sets without reverting back to absolute measurements.  It may be more valuable to use earned value analysis where progress is measured against a planned and budgeted schedule.

Percentages are often misleading

Where percentage is used for capturing progress reporting those updating reports are often prone to optimism bias.  Optimism bias is the tendency of individuals to expect better than average outcomes from their actions. In the context of rail infrastructure projects, optimism bias can lead to underestimation of project duration, overestimation of its benefits and underestimation of its total cost.

How often have you seen % complete very quickly rising to 90% and then staying there for weeks on end as the true extent of the works remaining is discovered?

No long term learning

As we capture and store increasingly large amounts of data from site there’s growing value in the insights that data may provide.  Consistently collected and structured to provide benchmarking information it’s invaluable for long term learning, cost estimating and understanding where productivity and efficiency gains may be made.  If data is only recorded on a percentage complete basis then we lose all these additional benefits.

In the rail industry there are recognised unit metrics which provide clear comparisons on business case value such as Single Track Kilometre (STK).  Capturing consistent structured data from site is the only way to confidently record and maintain these key industry metrics.

Percentage reporting is simple and well understood hence why it still proliferates the construction and engineering industry for reporting site data.  However, on its own, it provides no context and may lead to confusion as described above.  Most significantly when reporting by percentage we are missing out on short and longer term value in data.

Raildiary is the market leading solution for consistent, structured site data capture for commercial analysis and reporting.  We spend a huge amount of time with our users understanding their reporting requirements and creating structured data sources to ensure they gain maximum value from our platform.

Should percentage be banned from site data reporting? 5 reasons why you may agree

Will Doyle


I am an experienced RICS chartered Quantity Surveyor​ with first-hand experience of how the consistent capture and analysis of data can transform global project delivery.

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