Scientific Determination of Allowances
Define time allowances, document their calculation basis and avoid counting rest or delays twice.
Updated:
Allowances incorporate defined elements into normal time to establish standard time. Sampling can estimate proportions of selected activities or interruptions, but does not physiologically measure fatigue or determine how much recovery an individual needs. That requires ergonomic and occupational-risk assessment of actual job conditions.
Start with the percentage denominator
Do not mix two conventions:
- If a is an allowance relative to normal time: Standard time = Normal time × (1+a).
- If A is a fraction of total standard time reserved for the included elements: Standard time = Normal time / (1−A).
Ten normal minutes plus 15% of normal time gives 11.5 minutes. Reserving 15% of total standard time gives 10/0.85 = 11.765 minutes. Equivalent conventions satisfy a=A/(1−A). State the denominator and avoid adding breaks or contingencies already included.
Define observable categories
Possible states include direct work, preparation, technical interruption, scheduled break, personal needs and other. Decide whether setup belongs in the normal cycle or allowance to prevent double counting. Do not label a visible pause “accumulated fatigue” without supporting measurement. A snapshot cannot establish unjustified idleness either.
Verify causes separately through interviews, job assessment and records. Applicable reference tables may provide a starting point; do not assume that all ignore cognitive load or that observed break percentages replace them.
Sample size and precision
To plan a proportion under independent Bernoulli observations:
n = ceiling[z²p₀(1−p₀)/e²]
With z=1.96, p₀=0.5 and e=0.03, plan 1,068 records. With p₀=0.15 and e=0.03, plan 545. These are absolute three-percentage-point margins, not 3% relative error. The final interval depends on observed proportion and design; repetition, clustering and coverage matter. There is no universal requirement for more than 3,000 observations.
Random schedules do not eliminate observer reactivity. Explain the purpose; do not apply automatic correction factors or discard days showing inconvenient patterns.
Simulated example: compare compatible denominators
Assume 3,000 independent readings using agreed definitions:
| Observed category | Records | Percentage |
|---|---|---|
| Personal needs | 174 | 5.8% |
| Recorded pauses | 252 | 8.4% |
| Technical interruptions | 123 | 4.1% |
| Remaining activities | 2,451 | 81.7% |
The first three categories sum to 18.3%, with an approximate normal 95% margin of 1.38 percentage points for the aggregate. This does not establish that 18.3% is necessary, sufficient or attributable to fatigue. If a standard reserves 12% of total time for exactly the same elements, the descriptive difference is 6.3 points. If that 12% applies to normal time, first convert it: it corresponds to 10.71% of the total.
Investigate conditions and causes before changing standards. If competent assessment agrees on A=0.183 of total time, ten normal minutes would give 10/0.817=12.24 minutes; that calculation does not validate the selection of A.
Prevention, rights and the tool
Spain's Occupational Risk Prevention Act establishes preventive duties. A 95% sample does not certify compliance, sufficient court evidence or a safe work pace. Review risk assessments, collective agreements and participation by affected people with competent professionals.
WorkSamp supports state planning and recording. Results may inform investigation, but are neither a health diagnosis nor an automatic fatigue-assessment module.
References
NIST: proportion intervals. Spain's Occupational Risk Prevention Act.