SEO & PPC Metrics – Website Page Depth
When managing an SEO initiative or PPC campaign, one of the more challenging aspects is measuring the lead quality of the inbound visitors. Most people know how to measure Return on Investment (ROI) and Return on Ad Spend (ROAS), but that should not be the only metric used to evaluate the quality of the leads coming from different Search or PPC Engines. One of the best metrics for measuring lead quality is Page Depth.

Page depth is simply the average amount of pages a visitor sees during a session on your website. It should be fairly obvious that higher page depth is better than low page depth, but how to figure the metric correctly and determining a page depth baseline can be a bit more involved. For this exercise we will look at some actual PPC data from a major online retailer, but first let’s talk about how to measure page depth accurately.

We know minimum page depth must be 1.0 as it is impossible for any visitor to see less than 1 page. Most people would think page depth is simply calculated by: (Total Number of Page / Number of Visitors). While this is correct in the general sense, page depth should be adjusted to eliminate shopping cart pages. Let’s look at a hypothetical example before proceeding to an actual data set.

Suppose your website showed 10,000 pages last month to 2,000 visitors. Let’s also assume that your website converted those 2,000 visitor into 200 sales. Finally let’s assume that your shopping page is 3 pages long (this means that it takes 3 pages to fill out personal & billing info, and a confirmation page).

Using the traditional Page Depth formula, Page Depth would be calculated as:
10,000 pages / 2000 visitors = 5.0 Page Depth

Now let’s look at a calculation for page depth that adjusts the page depth calculation to remove shopping cart pages. The reason for this is that visitors who convert are forced to view 3 more pages, 1 of which (the confirmation page) is completely superfluous. The reason for this is that these pages do not measure the depth of a visitor’s session because they happen after the visitor has converted. Page depth as a metric should measure how far into a site a visitor goes regardless of conversion or no conversion. What Page Depth should be measuring is how conducive your website is to dispensing information about products or services you offer. Also, service websites typically do not have a shopping cart while e-commerce site do. By adjusting page depth to exclude shopping cart pages, page depth can be compared between types of sites without a shopping cart bias “helping” e-commerce sites.

So let’s do the Page Depth Calculation again and exclude shopping cart pages:
(Total Pages – (Conversions * Shopping Cart Page Length)) / Visitors
(10,000 – (200 * 3)) / 2,000 = 9,400 / 2,000 = 4.7 Page Depth

Notice that page depth dropped from 5.0 to 4.7 using the adjusted page depth formula. However this 4.7 pages calculation tells us that any average visitor will typically see 4.7 pages before either leaving or converting. If the 5.0 figure were used, it would be skewed by shopping cart pages that happen after the visitor has already been converted. Also all we could say for certain is that visitors who do not convert see less than 5 pages and those that do convert see more than 5 pages, but it does not tell us what the average visitor sees whether they convert or not. If you have a long shopping cart process or if you were to convert a high percentage of visitors, the traditional formula of [Total Pages/Total Visitors] would become even more skewed. The adjusted page depth calculation gives a more accurate indication as to how many pages a typical visitor views since we do not know beforehand if they will convert or not.

Developing a baseline page depth figure should be done over time and should be done for each engine or campaign separately. You will also have an overall page depth figure for all campaigns but by using this figure it will be more difficult to spot meaningful fluctuations as high traffic campaigns will be weighted far more heavily in the overall Page depth figure. One month is a good amount of time to collect data in order to calculate reliable Page Depth figures for each natural and PPC campaign. However, there are red flags to look for that can indicate a problem in less time than a month.

Let’s look at the PPC campaign data from a major online retailer doing around $10 million in gross revenues.

Notice the Raw (Unadjusted) Page Depth Figures for Kanoodle & Enhance [Not surprisingly, this figure also happens to be the adjusted Page Depth as neither engine converted a single visitor]. Enhance has a page depth of 1.34 and Kanoodle a rather unbelievable 1.10! Kanoodle’s Page depth figure says that for every 10 people that visit the site, 9 of the 10 bounce (Bouncing is a visitor who sees only the landing page they are directed to and then leave), and the tenth sees a second page and then bounces! This is the telltale sign of poorly qualified traffic or click fraud. Be aware that the smaller PPC engines and Shopping feeds are notorious for click fraud. Among these would be Kanoodle, Enhance, & Findwhat. Not only do they send unqualified traffic, but many of them also charge for 200-300% more clicks than any analytic program tracks. The Page Depth metric is an excellent tool for spotting these types of fraudulent traffic sources. Statistically speaking, it is highly unlikely for any visitors to convert from sources that generate a raw(unadjusted) Page Depth of less than 3.0. Why? Well because most e-commerce site have anywhere from a 2-5 page shopping cart, so a raw Page depth of less than three indicates that few if any visitors from that sources are making it to or through the shopping cart. If they were converting, raw Page Depth would have to be higher due to the additional pages a shopping cart adds to the page depth metric.

Hopefully this gives you an idea on how to calculate and use Page Depth as a significant metric when evaluating your campaigns. Remember, that it could be your site’s architecture (confusing navigation), bad landing page choices, or your site’s appearance that could be hindering visitors from seeing more pages. Assuming that there are no appalling usability issues plaguing your site, Page Depth can be an invaluable tool for measuring the quality of leads coming from your different traffic generating sources. Being that it is a simple calculation to gain Page Depth figures, take an hour or so and examine this metric to determine which campaigns are working for your site, and which are simply trying to get into your wallet.