A brief explanation of how search engines index and rank web pages are given here for clarity. Search engines are companies that send programmes (called crawlers, robots, bots or spiders) to crawl the Internet, collecting the content of every web page they visit. This information is stored in an index (a complex database) for later use. When a user specifies a search query, the search engine algorithm examines the query, tries to determine what is that the user wants and then matches this information need as best it can with the website content it has stored in its index. The results are shown on the user’s screen. Because there are almost always more than one possible answer, the search engine also has to decide in what order to display the answer, with the most relevant answer at the top (Weideman 2009).

Commercial motives coupled with inherent human laziness prescribes that the first few results on the results page are the ones that will receive the highest number of views. This has spawned the SEO industry, where websites are designed with search engine crawlers in mind, trying to ensure that every important web page will rank highly for a given search query. SEO techniques are divided into on-page and off-page types. On-page SEO refers to changes a webmaster can make to the web pages under his or her control, where off-page techniques include things to be done outside the website at stake, to improve its ranking. Also, web page text must be written in an ‘SEO-friendly’ way, enabling crawlers and algorithms to easily detect what a given web page is really all about. On-page SEO includes the writing of ‘good’ meta-tags, Alt text for images, the correct use of H1 tags, well-written anchor text, file-name choices and others. Off-page SEO is mostly about creating an ‘awareness’ of the website at stake by building in-links (hyperlinks pointing from other website to the main website), and ensuring that many references about the main website are spread across the Internet. Unfortunately, the SEO industry also has its dark side – so-called black hat SEO is being practised, for example, by overstuffing a web page with keywords to appease the crawlers (Zuze & Weideman 2013).

To ensure a higher volume of human visitors, websites need to be visible to search engine crawlers. One important element in high rankings is how closely the contents of any given web page match the specification of a search engine for a ‘good’ website. This match is determined by a search engine algorithm. A process termed SEO can be used to improve how closely a website’s layout matches the guidelines of the search engine. This process includes writing good content, ensuring a high number of links pointing to the website, plus many other factors. These are sometimes classified as either:

SEO is theoretically a once-off process because these changes will remain on the website after being implemented. However, the SEO done on a website must be updated over time. Search engines change their algorithms regularly, and competitor websites with high rankings could push down a given website on the SERPs.

SEO mostly involves a relatively large investment when done for the first time, with a much lower expense over time after that. Much research has been conducted to determine the best strategy to leverage SEO into ranking better on Google. Luh, Yang and Huang (2016) claimed that important keywords on the website should be incorporated into the URL, the page title and the snippet. Both Sullivan (2016) and Weideman (2009) have developed models to rank the SEO elements used by Google algorithms in the commercially important ranking of results on SERPs. However, many large retrieval systems suffer from low efficiency because of badly designed systems (including the ignorance of SEO principles), which makes it difficult for search engine crawlers to find information and return relevant results (Weideman 2015).

According to Yang et al. (2012:1141), there has been tremendous growth of search auctions when, as these authors put it, ‘economics meet search’.

The same authors continue and explain that search auctions (or PPC) have now become one of the most used online advertising channels. So much so that search auctions now produce the primary revenue source for major search engines. Google has reported a total revenue of $8.44 billion in the fourth quarter of 2010. Of this total, search auctions contributed 97% (Yang et al. 2012:1141). Prior research has been conducted to reduce the negative effect of inefficient keyword bidding when running a PPC campaign (Nabout 2015).

Some studies have shown that, when faced with the choice, more users will click on SEO results than those clicking on PPC results (Neethling 2008; Panda 2013). This seems to confirm the existence of an anomaly as noted by Kritzinger and Weideman (2015). However, the PPC industry has grown into a multibillion-dollar industry and generates a large income to its hosts, including Google and Bing (Gupta & Mateen 2014). This implies that the PPC system is successful and that it should be investigated.

The CPA is an indication of the advertising cost of converting a human visitor into a paying client, producing revenue for the company. Ideally, the CPA should be low, which implies a higher profit rate. It has been claimed that acquiring a new customer could cost five times more than that to retain an existing one (Pfeifer 2005). This confirms the importance of determining which marketing method produces the lowest CPA.

For Website 1, the test period was from 07 September 2015 to 05 December 2015. The total number of organic clicks (SEO clicks) was retrieved from Google’s Web Console.

Figure 3 indicates that Website 1 received 56 334 clicks from organic search results over the test period. This resulted in 57 475 organic sessions. The organic sessions were retrieved from Google Analytics (see Figure 4).

From the 57 475 organic sessions, the website analytics recorded 219 e-commerce transactions with a total revenue of R314 078.50, as shown in Figure 5.

Website 1 received 28 926 clicks from the Adwords Campaign (PPC Campaign) – this produced 29 795 PPC sessions. From these sessions, a total of 178 transactions were recorded over the 3-month period. This produced a PPC revenue of R238 925.60 (see Figure 6).

To summarise the results for Website 1, refer to Table 1.

The values in the PPC and SEO columns were extracted from the Google Analytics records, while the Ratio column figures were calculated as a ratio of the previous two column values. Figures in the Ratio column were rounded to one decimal place. In all cases, a decision was taken in terms of how the ratio was to be calculated, to enable easier interpretation of the table data. For any given two sets of figures, a ratio of 1 (1:1) would mean that SEO and PPC performed identically. It was decided randomly (because only the ratio and not the actual figures matter) that if the PPC and SEO figures for a given row indicated that SEO performed better than PPC (e.g. SEO produced more clicks, or SEO cost less than PPC), then the calculation would be performed in a way that the ratio would be above 1. This would allow for easier interpretation of results because a figure higher than 1 would always signify ‘better’ for SEO and ‘worse’ for PPC.

When considering the values of Table 1, note that higher values are more desirable than lower ones: Clicks, Sessions, Pages/session, e-commerce conversion rate, Transactions and Revenue. The remaining measures need to be lower to be better: Cost, Cost per click (CPC), Bounce rate and CPA. This difference is merely a result of the way these metrics were designed to indicate a given value for a given attribute. More clicks, more transactions and higher revenue are better, while lower values for expenditure (costs) and unimpressed users are better.

The figures in Table 1 can be classified into two types:

From Table 1, over the test period of 3 months, a combined cost of R84 918.68 was incurred. PPC represents 68% of the total cost, while SEO represents the remaining 32%. The total number of clicks received was 85 260. SEO represents 66% of the total clicks, while PPC represents the remaining 34%. This is almost the exact reverse of the cost split between PPC and SEO.

Also from Table 1, the CPC for PPC was R1.99 and for SEO was R0.48 for SEO – the CPC for SEO is four times lower than the CPC for PPC. The bounce rates for PPC and SEO were relatively close to being the same at 29.61% and 23.59%, respectively. The e-commerce conversion rate for PPC is slightly higher than that of the SEO e-commerce conversion rate, at 0.6% and 0.38%, respectively. This indicates that PPC visitors are slightly more likely to convert than those arriving on a site through SEO results.

Finally, when comparing the total revenue, it was found that PPC resulted in R238 925.60 (or 43%) of the total revenue received over the 3-month period. SEO resulted in R31 4078.50 (or 57%) of the total revenue.

In summary, three of the calculated ratios are indicative and two of the three favour SEO. This includes the most important measure, the CPA.

For Website 2 the test period was from 17 January 2016 to 15 April 2016. The total number of organic clicks (SEO clicks) was retrieved from Google’s Web Console (see Figure 7).

As can be seen from Figure 7, Website 2 received 3 871 508 clicks from organic search results over the test period. This resulted in 4 872 537 organic sessions. The organic sessions were retrieved from Google Analytics (see Figure 8).

From the 4 872 537 organic sessions (see Figure 8), the website received 41 186 e-commerce transactions with a total revenue of £2 163 584.37 (see Figure 9).

From the Adwords Campaign (PPC Campaign), Website 2 received 322 483 clicks, which resulted in 442 399 PPC sessions. From the 442 399 PPC sessions, a total number of 7869 transactions were recorded over the 3-month period, which resulted in a PPC revenue of £354 876.22 (see Figure 10).

For a summary of the results for Website 2, see Table 2.

From Table 2, the authors found that over the test period of 3 months a combined cost of £88 966.82 was incurred. PPC represents 96% of the total cost, while SEO represents the remaining 4%. In contrast, the total number of clicks harvested over the 3-month period was 4 193 991. SEO represents 92% of the total clicks, while PPC represents the remaining 8%. This is almost the complete reverse of the cost split between PPC and SEO.

From the numbers in this table, it became clear that the CPC for PPC was £0.27 and £0.00087 for SEO. The CPC for SEO is significantly lower than the CPC for PPC. The bounce rates for PPC and SEO were very different at 59.55% and 26%, respectively. The e-commerce conversion rate for PPC is higher than that of the SEO e-commerce conversion rate – 1.78% and 0.85%, respectively. This means that PPC visitors are slightly more likely to convert.

Finally, when the authors compared the total revenue, it was found that PPC resulted in £354 876.22 (or 16%) of the total revenue received over the 3-month period. SEO resulted in £2 163 584.37 (or 84%) of the total revenue.

In summary, three of the calculated ratios are indicative, and two of the three favour SEO. This includes the most important measure, the CPA.

For Website 3, the test period was from 8 September 2015 to 6 December 2015. The total number of organic clicks (SEO clicks) was retrieved from Google’s Web Console.

As can be seen from Figure 11, Website 3 received 296 101 clicks from organic search results over the test period. This resulted in 319 660 organic sessions. The organic sessions were retrieved from Google Analytics (see Figure 12).

From the 319 660 organic sessions, the website received 1573 goal completions (see Figure 13).

From the Adwords Campaign (PPC Campaign), Website 3 received 59 838 clicks, which resulted in 19 572 PPC sessions. From the 19 572 PPC sessions, a total number of 811 goals were recorded over the 3-month period (see Figure 14).

To summarise the results for Website 3, see Table 3.

From Table 3 the authors found that over the test period a combined cost of R315 592.29 was incurred. PPC represents 88% of the total cost, while SEO represents the remaining 12% of the total cost. In contrast, the total number of clicks received over the 3-month period was 355 939. SEO represents 83% of the total clicks, while PPC represents the remaining 17%. This is almost the complete reverse of the cost split between PPC and SEO.

From the figures in Table 3, the authors also found that the CPC for PPC was R4.68 and R0.13 for SEO. The CPC for SEO is 36 times lower than the CPC for PPC. The bounce rates for PPC and SEO were also very different at 66.73% and 41.29%, respectively. The goal conversion rate for PPC was higher than that of the SEO goal conversion rate – 4.14% and 0.49%, respectively. This means that PPC visitors are significantly more likely to convert.

In summary, three of the calculated ratios are indicative, and two of the three favour SEO. This includes the most important measure, the CPA.