Mobile Vs Desktop – PPC Cross-Device Testing   

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Should you be pushing more traffic to your mobile site via PPC? What results can you expect from a mobile campaign? And what type of campaign is most likely to succeed? ClickThrough’s paid search specialist Ian Boyden recently conducted a cross-device test on key client accounts to measure the effect of mobile advertising on conversion. Here, he shares his findings

Google have been predicting mobile search queries will overtake desktop for quite some time. For some of our clients it seems to be happening already, especially at the weekends and during key seasonal events like Christmas week or Easter Bank Holiday weekend. This is because most people are at home and it is easier to reach for a mobile device rather than turning on a desktop computer.

At present, many marketers believe consumers don’t convert via mobile – but they are aware of evidence showing that mobile is a key tool for consumers researching before they buy on a different device. As the majority of PPC campaigns measure conversions on a last-click basis – it is mobile devices that are seeing the worst conversion rates. As a result, a lot of AdWords accounts have low mobile bid modifiers implemented and the scope of the account is being severely hindered.

If a consumer starts researching on mobile but then goes on to buy via another device then surely the mobile portion of their journey has proved vital to the conversion? We wanted to prove the value of mobile advertising and its effects on multi-device conversion rates to see if there really is a tangible link.

With this in mind, we decided to conduct a test on seven key PPC accounts over a one month period. Do people really research on mobile and then convert on desktop? This is what we wanted to find out and a cross-device test is the best way to do this.

Conducting a Cross-Device Test

A cross-device test is a quick and easy way of comparing an aggressive mobile strategy versus a traditional strategy where mobile sees little or no traffic. As this is carried out on the same keywords during the same time period, the test provides a comparison not influenced by seasonality or other external factors. What we would expect to see is higher volumes of traffic coming through as a result of the mobile push and potentially a higher conversion rate as consumers are able to research on mobile before returning well-informed ready to convert via desktop.

Laptop, tablet, mobile

We chose seven PPC accounts with a variety of target markets - some were e-commerce and some lead generation. Some accounts had good quality mobile sites and some didn’t. Some clients were already implementing 0% mobile bid modifiers and some were pulling mobile bid modifiers back, by up to 60% in some cases.

We chose one ad campaign per account. The campaign needed to be generating decent amount of data in order to make a comparison, and it was important they did not include brand keywords.

We then duplicated the ad groups to give us a ‘control’ and a ‘test’ group. The control ad groups had 0% mobile bid modifiers and the test ad groups had 60% bid modifiers.

We used the tool AdWords Experiments to split impressions 50/50 between each ad group and ensured that keyword bids and creatives were kept symmetrical in each ad group. The experiment ran for four weeks.

Cross-Device Results

Out of the seven accounts tested, three of them saw the test ad groups achieve higher conversions as a result of pushing the mobile bid modifier. One client saw the conversion rate increase by 33% after pushing mobile.

33% conversion rate increase


For all seven clients, the mobile bid modifier resulted in 5% more traffic. However, the conversion rate dropped by 22%, which affected the cost per acquisition and ROI. CPCs remained somewhat static, at 6% higher.

Mobile Conversions graph

For accounts where we did see improved conversions, a common theme was the fact that the conversions still weren’t coming from mobile on a last click basis. The vast majority of conversions still ended on desktop or tablet. However, the results did indicate that pushing mobile is helping to start the path to conversion.

Result Highlights

One e-commerce client saw 61% more conversions. However, the average order value on the mobile ad group was much poorer, which led to a 70% lower ROI. This needs to be taken into account if deciding to run this test.


Another client saw fewer bookings when mobile was pushed, despite the lead conversion rate staying similar – could mobile be driving a lower quality of lead which fails to then generate bookings?

Another e-commerce client also saw negative results from this test, the client has a target market of consumers aged 65+. Could this potentially be a reason why performance was poor as an older demographic are less likely to use mobile devices? Clients need to consider target audience / buyer personas and their technology vehicle of choice when deciding if a mobile push is relevant.

For another e-commerce brand with multiple branches around the UK, despite there being less on-site transactions after pushing mobile, they saw a large increase in visits to the store locator page on the website. This could be a clear indicator that consumers use mobiles more to research online before ultimately finding their nearest store and making a purchase. We are working with some of our clients to prove this relationship between online and offline.

Importance of Mobile Optimisation

Google launched its mobile-friendly algorithm on April 21, 2015. This has encouraged more website owners to optimise their site to work cross-device.

From our cross-device test, we found that the best performers had a strong, optimised for mobile website, which allows consumers to research and evaluate the products on offer.

This is something to bear in mind if considering a cross-device test. If your website is already optimised for mobile then a push on mobile bid modifiers will probably have a bigger impact.

Cross-Device PPC - What Next?

  • Try running a cross-device test on one of your PPC campaigns - it is easy to set up and the results gained could prove valuable when you sit down to establish your PPC strategy for the year ahead. If you can prove there is extra volume up for grabs then this should be considered when setting your PPC budget.
  • Bear in mind that 0% bid modifiers on mobile should be the default for most of your campaigns. However, controlled tests like this one are great at providing evidence for whether or not this should be the case.
  • Mobile friendly ads or click to call extensions are obviously needed if you are starting to see higher mobile traffic levels on your site.
  • Consider using third-party tools, like Kenshoo, which allow you to change mobile bid modifiers at certain times of the day. We found that mobile searches peak first thing in the morning. This is because people often use their mobile on their commute into work. Therefore having high average positions makes sense at this time of day. You will probably see that the majority of consumers will return to your site later in the day to convert on a different device.

In summary, mobile is a really important start to the consumer journey – it is not just about the last click. As PayPal, Apple Pay and the like work to make purchasing by mobile easier and more secure, mobile conversions can only grow. Future-proof your marketing plan – optimise for mobile.

Keen to attract more mobile traffic but not sure how to push mobile bid modifiers or even if it’s right for you? Contact us

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