Short answer

For each weekday, divide consistently defined deviations by eligible completed runs. Raw counts can mislead when denominators differ. Match date, route, vehicle, load and record coverage; even a repeating weekday pattern does not prove the day is the cause. Track the same fields in the next period and document what changes.

If one weekday appears to have many deviations, first compare the number of eligible runs on that day.

Add the weekday. Add run date and weekday to each row, and use the same deviation definition for every day.

Use a rate instead of a raw count

Set the number of eligible runs for each day.
Count deviations identified by the same rule.
Divide deviations by eligible runs and record the rate.
Flag runs with missing records or that are not comparable.

Why weekdays may look different. Run volume, route, vehicle, load and record completeness may vary by day; do not attribute the difference to the calendar without measuring them.

Narrow the comparison. Where possible, compare runs on the same route with similar loads, and record how many observations remain under those conditions.

Next period

Calculate the next period's rate using the same definition and denominator rule; note any difference in coverage from the prior period.

Tie the result to a record

Note the observed relationship without presenting it as a cause; set the measure to follow and a review date.

Comparing deviations on the same weekday

Short answer

Use a rate instead of a raw count

Next period

Tie the result to a record

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