An emergency department requested a study of laboratory turn-around times.

To obtain the most reliable laboratory turnaround time (TAT) data for an emergency department, sampling must be representative of the full operating reality , not concentrated only in one high-volume window. Although the review shows peak arrivals during weekend evenings , TAT performance is influenced by multiple time-dependent factors: staffing levels in the ED and lab, specimen transport coverage, analyzer workload, competing inpatient priorities, courier schedules, and shifts/hand-offs. If sampling occurs only on weekend evenings (or only on weekends), the study risks systematic bias by over-representing peak congestion conditions and under-representing baseline performance during non-peak periods.

Therefore, sampling across varied weekday and weekend hours produces the most reliable dataset because it captures both peak and non-peak operations, different staffing patterns (day/evening/night), and weekday-versus-weekend workflow differences. This broader sampling supports stronger conclusions about true average performance, variability, and whether delays are isolated to peak demand periods or occur across the week. It also enables better root-cause analysis (e.g., shift-related bottlenecks, transport gaps, batching behavior) and more credible improvement recommendations. Random weekend-only sampling or intermittent peak-only sampling may be easier, but it is less representative and therefore less reliable for organization-wide decisions.