Saturday, Jun 3, 2023

Verifying phone numbers in the UK

Whether businesses, RDD, mobile lifestyle, or landline lifestyle, we love phone numbers here at Sample Answers. In this blog entry, we’ll provide a..

two purple telephones on a wall

Whether businesses, RDD, mobile lifestyle, or landline lifestyle, we love phone numbers here at Sample Answers. In this blog entry, we’ll provide a brief, informational look at the importance of verifying phone numbers, and how phone numbers connect to what we do.  

Let’s start with mobile phone numbers. Whilst we have access to around 17 million of the UK’s households, it’s important to note that phone number allocation and creation are in a constant state of flux and are dynamic. People move homes and change mobile providers on a whim, and businesses rise and fall. This makes for an incredibly competitive commercial landscape, never standing still.  

As an example, there is an impending mobile phone number shortage in the UK, with 11-digit number blocks prefixed with 07 in short supply. Ofcom assigns mobile numbers to UK network providers in blocks of 1,000. EE, Virgin, O2, and others then assign these numbers to new customers as needed.

Consequently, Ofcom has a strict ‘use it or lose it’ policy regarding Pay As You Go (PAYG). This means an operator has the right to withdraw any unused service or number and re-allocate it to make sure the number distribution is completed efficiently and effectively. This policy coincides neatly with a recent strategy of network providers sending out free PAYG SIM cards with pre-assigned numbers to their customers.

Many of these pre-assigned numbers are never activated, and in turn there’s an expanding volume of allocated numbers that remain dormant for re-purposing. Providers such as Vodafone and O2 operate with terms of 90-365 days for re-allocation of PAYG numbers. In short, that’s an awful lot of churn.

Regarding landlines, we know that at least 5% of households move to another city or county in a given year. This fact alone means 5% of a random landline sample of lifestyle data will be inaccurate due to being out of date. Of course, once we start to consider other factors such as data-collection error, deaths, and so forth, then the picture looks worse.

All of this means that as a sample provider, we need to be on our game to keep providing the most accurate phone samples possible.  Let’s take a look at this through a typical count (below):

chart displaying UK mobile users 18-21 years across different regions


We know from experience that if we do not validate the phone numbers before sending them to our clients, 25%-30% of the phone numbers will be either disconnected, turned off, in a draw (like my parents’ mobile), or otherwise unusable. Put simply, this is too much of an error either for us to tolerate – or for our clients to overcome – when they start dialing the sample and collecting data. Whilst we have to be mindful of any gap in volumes from count through to delivery, we have a reliable understanding of what the percentage of “dead” records will be and our clients can work around that.


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Regarding landlines – be it RDD or lifestyle – Sample Answers is fortunate enough to work with a telecoms engineer who checks for working numbers without having the owner’s phone or handset ring. This is vital for a) returning working numbers only and b) preserving the privacy of the household at the other end. Indeed, back in the early 2000s, Ofcom was alert to the nuisance nature of a lot of phone number testing, the use of automated dialing, and the silent/ghost calls that dialers caused.  

Mobile phone numbers are also verified – but in a different way. Partnering ultimately with telecoms providers, we are able to screen both our lifestyle and RDD mobile numbers against centrally held databases that register – anonymously* – mobile phone signals. If, for example, you set your phone to flight mode when you go to the cinema and switch it on again after the film is  finished, this is registered. Likewise when a train enters a tunnel, causing a temporary loss of mobile signal that is restored once the train exits the tunnel. Like it or loathe it, your phone is more or less constantly sending a signal, so we know within 24 hours of recency if a mobile phone number has been active, not just hidden in a drawer.  

We clean phone numbers before delivering all consumer samples so our clients can be confident in the quality, and therefore the connection rates, they need in order to deliver data-collection and research projects on time and on budget.  

*This is one of the reasons it’s not possible to provide mobile RDD based on a respondent’s location.

The post Verifying Phone Numbers in the UK first appeared on GreenBook.


By: Martin Cawley
Title: Verifying Phone Numbers in the UK
Sourced From:
Published Date: Fri, 04 Feb 2022 12:00:55 +0000

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