When a campaign's conversion rate drops, the first thing examined is the copy, then the agent's script, then the calling hours. The list itself is almost never treated as a suspect.
Yet in a three-year-old customer list, a share of the numbers no longer works: the line was closed, the number was reassigned, the person changed it.
The cost of a dead number
A dead number is not merely a wasted call:
- It distorts campaign reporting, inflating the "unreachable" rate and making the agent look worse than it is.
- Retry rules mean it gets called several times, multiplying the cost.
- If the number was reassigned, you are calling a complete stranger. That is not a cost line, it is a reputation risk.
The power of a random sample
You do not need to call an entire list to measure its health. Picking two hundred records at random and examining only those gives a reliable picture of the whole.
One detail is critical: the sample must be random. Two hundred records taken from the top of the list mislead, because in most systems lists are ordered by date and the top records are the oldest — therefore the most degraded. The reverse is equally true: a sample from the bottom shows the newest, healthiest records and flatters the list.
The right indicator to measure
Some flags systems provide are unreliable for measuring reachability. A call marked "answered" does not guarantee a human was there, and the existence of a recording file does not mean a conversation happened.
The most reliable indicator is duration: a call length greater than zero shows the line genuinely opened and something was said. When measuring campaign health this single field misleads less than any other flag.
Cleanup rules
When cleaning a list, marking beats deleting; a deleted record never comes back, while a marked one can be reviewed later.
Rules that work:
- Called three times, never picked up → mark inactive, remove from campaign lists.
- Received an invalid number error → inactive immediately; that error is permanent.
- No contact on any channel for over a year → move to a separate pool; a win-back attempt can precede deletion.
- The same number on multiple records → merge. Duplicate records are the most common reason for calling the same person twice.
Prevention for incoming records
Cleanup is not a one-off; the list gets dirty again every day. Two controls at the entry point reduce future cleanup:
- Normalise number format on capture. One form, with country code, no spaces. Two spellings of the same number are the source of duplicates.
- Do not create a new record when the number already exists. Updating the existing record always beats adding a row.
When to run a cleanup
Before large campaigns. A cleanup after the fact does not refund calls already paid for. Half a day of cleanup before a campaign usually lowers the number of people to call and raises the number of people reached — both at once, which is a good sign.
Tomorrow: the most misread output of post-call analysis — what the score actually measures.