What are leading and lagging metrics in maintenance?

Maintenance metrics are used to measure and quantify the level of achievement of a particular asset or plant process. Determining the state of the plant using metrics and performance indicators enable personnel to make data-driven decisions and identify potential problems. Metrics and indicators are generally classified according to whether they predict future performance or describe past performance – these are referred to as leading or lagging indicators, respectively.

Leading indicators
Leading indicators are measurements that predict the outcome of a process or an event. These indicators are measured and are considered to be precursors of events or situations.

An example of a leading indicator is schedule compliance, when regarded as an indicator of the likelihood that an asset will experience unplanned failures and downtime. Because schedule compliance describes the amount of planned maintenance activities done on time, it can be correlated with how effectively maintenance activities are carried out, and therefore relate to increasing reliability.

Similarly, the metric planned maintenance percentage can be considered as a leading indicator as it affects the amount of unplanned downtime by aiming to keep assets running at optimal health. It also affects the required manpower as planned maintenance activities can be more efficiently scheduled.

Lagging indicators
Lagging indicators measure the performance of the plant by looking at the outcomes and results of processes and operations. By analyzing the historical trend of the performance of the plant and its parts, reactive strategies can be applied to address underlying issues.

Examples of lagging indicators include mean time to repair (MTR)mean time between failure (MTBF), and overall equipment effectiveness (OEE). Notice how these metrics are measured to confirm trends that have developed over time. Because these metrics are basically a historical record of performance, they can provide insights on which events in the past might have caused fluctuations to the plant’s performance.

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Using leading and lagging indicators
From the previous discussion, you can imagine how one indicator that predicts the future and another that looks back at the past, can form a complete view of the performance of the plant over time. Leading and lagging indicators, together, aim to provide a panoramic view of the state of the plant through time.

The plant’s maintenance manager is expected to identify a manageable set of key performance indicators (KPIs) – a mix of leading and lagging indicators viewed as a whole picture – to assess the plant’s maintenance effectiveness.