Psychological delta

The performance you are hiring for is already on your payroll

Roughly half of the differences in job performance sit inside the same person — between their better and worse weeks — not between one person and the next. Hiring cannot reach that half. This page is about the half that is already yours.

The Gap Inside You

Filmed September 2026, after presenting this research at the XIX Vanguard Scientific Instruments in Management conference.

40–65%
of the differences in job performance sit inside the same person, not between people

18%
is what the strongest hiring procedure we have — the structured interview — predicts about the differences between people

71%
of lost productive time comes from people who are at work but performing below their level, not from absence

The psychological delta

I call that within-person half the psychological delta. It breaks into four quantities you can actually observe in your own organisation.

Δ-peak

the distance from a person’s typical day to their best day. This is the reserve. Unlike a candidate’s potential, it is not a prediction: the good days have already happened, in your organisation, on this job.

Δ-total

the full range, read together with the average. A wide range around a high average is flexibility. A wide range around a low average is exposure.

Δ-floor

the distance from typical down to their worst day. This is what fatigue, stress and friction cost, and it is where presenteeism is paid for.

Recovery

how fast the person returns to their typical zone after a bad stretch. Of the four, this is the one leaders influence most and measure least.

Δ-peak

the distance from a person’s typical day to their best day. This is the reserve. Unlike a candidate’s potential, it is not a prediction: the good days have already happened, in your organisation, on this job.

Δ-floor

the distance from typical down to their worst day. This is what fatigue, stress and friction cost, and it is where presenteeism is paid for.

Δ-total

the full range, read together with the average. A wide range around a high average is flexibility. A wide range around a low average is exposure.

Recovery

how fast the person returns to their typical zone after a bad stretch. Of the four, this is the one leaders influence most and measure least.

One person, sampled over time: the typical level, the peak and the floor, the two distances that make up the delta, and the time it takes to return. Illustrative series.

The sentence to keep.

In a labour market where nearly three in four employers cannot buy the performance they need, the largest untapped source of performance is not on the market at all. It is the distance between the versions of the people already hired. The well is not in the town. It is in the yard.

Sources: Dalal, Alaybek & Lievens (2020), Annual Review of Organizational Psychology and Organizational Behavior · Stewart & Nandkeolyar (2006), Personnel Psychology · Sackett et al. (2022) and Sackett, Zedeck & Fogli (1988), Journal of Applied Psychology · Stewart et al. (2003), Journal of Occupational and Environmental Medicine · Mark, González & Harris (2005), CHI · Arthur et al. (2003) and Lacerenza et al. (2017), Journal of Applied Psychology · Frazier et al. (2017), Personnel Psychology · Eurostat (2026) · Central Bank of Malta (Borg 2019; Grech 2023) · FHRD & PwC HR Pulse Survey 2025 · Balabanov (2025, 2026). Full reference list in the paper.