04 — Research · 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.
Watch
The Gap Inside You
A short talk on why the performance you are trying to hire is often already inside your teams — and how to reach it.
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 (range across studies)Dalal, Alaybek & Lievens (2020), Annual Review of Organizational Psychology and Organizational Behavior
- 18%
- of the differences between people is predicted by the structured interview, the strongest hiring procedure we haveSackett et al. (2022), Journal of Applied Psychology
- 71%
- of the cost of health-related lost productive time comes from people who are at work but performing below their level, not from absenceStewart et al. (2003), Journal of Occupational and Environmental Medicine — US study of health-related lost productive time
Synthesised in Psychological Delta (Balabanov, 2026). See the evidence →
The construct
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
- 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
- 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
- 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
- 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.
Tap a label above to see what each part means.
The sentence to keep.
In a labour market where nearly three in four employers struggle to fill the roles they need (ManpowerGroup, 2026), 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 paper
Psychological Delta: The Within-Person Performance Reserve and the Limits of the External Talent Market
By Alexander Balabanov, PhD (DynamixLab Ltd). Presented at the XIX Vanguard Scientific Instruments in Management conference, September 2026. The full paper follows once the journal's review is complete.
The argument in brief
When organisations need better performance, they almost always try to hire it. My paper argues that a large part of that performance is already inside the people they employ.
- Each person varies a lot. Measured week after week, roughly 40–65% of the differences (depending on the study) in job performance sit between a person's own good and bad days, not between people. The gap between someone at their best and at their worst is about as large as the gap between two colleagues.
- Hiring cannot reach that part. Selection compares candidates. It cannot decide how a new hire's good and bad days will go: that depends on workload, interruptions, stress and the climate in the team after hiring.
- The hiring route is narrowing. Bulgaria is short of people; Malta's foreign hires leave quickly; and external hires cost more and often start weaker than internal ones.
- Part of the gap can be reached. Some good days come from luck. But bad periods with preventable causes, such as overload, constant interruption, poor recovery or fear of admitting mistakes, can be reduced. I call that the addressable reserve.
- Reaching it is a management task: read each person's range, not just the average; protect attention; train in spaced sessions; make errors safe to admit; and use internal moves. Measurement serves coaching, never surveillance.
In one sentence: the performance you are trying to buy on the market is partly already on your payroll, in the distance between your people's good days and bad days.
A four-page executive brief, written for HR leaders in small, tight labour markets, is available to download below.
Download the executive briefPut it to work
Find out how much of the reserve your organisation can reach.
The Performance Reserve Diagnostic applies this research to your own teams in 3 weeks, starting with data you already hold.
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 · ManpowerGroup Employment Outlook Survey (2026) · Eurostat (2026) · Central Bank of Malta (Borg 2025; Grech 2023) · FHRD & PwC HR Pulse Survey 2025 · Balabanov (2025, 2026). Full reference list in the paper.