OPS.15.1:4.5 - Aggregate only compatible observations

Keep the population, event pair, clock and weighting rule consistent within the reported aggregate. Combine totals before dividing when group sizes differ. An unweighted mean of departmental means gives each department equal weight, not each case equal weight.

Choose the weighting from the question. A case-weighted mean describes a typical counted case. Resource-demand weighting describes a different burden. Retain classes when the proposed change affects them differently or an aggregate conceals a service commitment.

To compare policies, use the same recipient boundary unless changing that boundary is the point of the decision. If internal admission moves later, report upstream waiting together with internal residence before concluding that customers receive results sooner.

For uncertain or incomplete observations, derive the consequence still supported. A residence known to be between four and ten hours cannot decide an eight-hour criterion. It can already satisfy an upper limit of twelve hours under the same assumptions. Choose further observation through C.11.DUA; a complete history is not a prerequisite for every comparison.