CTR is the metric that Google pushes you to use the most as their ad rotation default is set to optimize for clicks, which is the highest click through rate ad. This metric is useful to use for ad testing when you want to increase traffic or one of your primary goals is visitors. However, as it does not take into account conversions or revenue goals, it is often not a great for sites that are trying to gain new customers from PPC advertising.

What is CTR?

CTR is simply the ratio of impressions to clicks.

How CTR is Calculated

CTR is calculated by diving the number of clicks by your impressions:

CTR = clicks/impressions

It is generally displayed as a percentage. Here are some examples:

Ad	Clicks	Impressions	CTR
1	45	243	18.52%
2	97	1023	9.48%
3	56	840	6.67%
4	32	230	13.91%

In this case, ad 1 has the highest CTR and ad 3 has the lowest CTR.

The Advantage of using CTR as Your Testing Metric

There are two main reasons to use CTR as your testing metric:

• Getting the most traffic possible
• Increasing quality scores

If your goal is to get more traffic, have more people see your site, then CTR is the best metric to use for testing. This is a common metric to use for brand departments who want to make sure that people are seeing their offer. It is also common to see companies use CTR for their branded keywords and another metric for their other keywords.

If you are struggling with Quality Score, then using CTR as an ad testing metric can often help in increasing Quality Score. As CTR is one of the most important factors in Quality Score, having high CTRs often correlates to higher Quality Scores (and often lower CPCs).  It is common to see an account where there is a direct correlation between CTR and Quality Score.

For instance, here’s a chart for one account where the metrics are broken up by Quality Score ranges. The trend between higher Quality Scores with higher CTRs is a very common occurrence.

Quality Score	Clicks	Impressions	CTR
1	0	0	0%
2	1	143	0.70%
3	21	3094	0.68%
4	1036	164,582	0.63%
5	471	23,289	2.02%
6	7563	353,377	2.14%
7	59,593	1,530,468	3.89%
8	68,153	1,435,300	4.78%
9	93,640	1,329,169	7.05%
10	131,586	1,472,395	9.62%
Totals	372,064	6,301,816	5.90%

Therefore, if your main goals are to increase Quality Scores or receive the most traffic, CTR is a good metric to use.

The Disadvantage of using CTR as Your Testing Metric

While  CTR is good for getting large amounts of traffic; what it doesn’t do is discriminate against good or bad traffic.

For instance, if you have a high CTR and a very high bounce rate; then you’re just attracting traffic that does not care about your message. Therefore, even when you are trying to get the most traffic possible, its best to use interaction goals (such as page views per visit or time on site) to make sure you are receiving quality traffic. Thus, CPI (conversion per impression) is a better metric to use than CTR when your goal is high quality traffic. With  CPI, you can set a goal based upon a quality visit and then optimize your ads to attracting the most qualified visitors as opposed to just the most visitors.

Raising CTRs to increase quality scores is good for most companies; but not necessarily all of them. In many cases you use your ads to qualify users before they click on your ad. If you remove the qualification, then your CTR and quality score will often increase, but at the detriment of your overall goals.

For instance, in the B2B (business-to-business) space, it is common to add qualifications to ads, such as an account adding “for businesses” or large commercial sales adding “industrial” to the ads. The goal of those qualifications is to clarify to the user that your offer is specific to businesses and not to consumers. When you remove those qualification, you do often see some metrics (Quality Score & CTR) increase, but your sales staff is generally unhappy as they aren’t receiving as many leads or the ones they do receive are not qualified.

Examining CTR is useful when combined with other metrics in order to break ties. For instance, if you have two ads with identical metrics (such as CPI, CPA, CR, ROAS) and you’re not sure what to pick, choosing the higher CTR ad will generally result in higher quality scores and thus slightly higher positions (so more traffic) or lower costs.

Conclusion

If you care about the quality of your traffic, the CTR is never a good testing metric to use. In those cases, you should use a goal (such as time on site) and CPI (conversion per impression) as your testing metric.

If you care about actual conversions, then CTR is never a good metric to use by itself as it doesn’t use conversions or revenue in its calculations.

If you are struggling with raising quality scores, then CTR can be a great metric to use in your testing.

CTR is important. Without clicks, you won’t receive any conversions and the other metrics are moot. However, CTR is rarely a metric you will use by itself in your testing, yet it is a great stat to use as a tie breaker when you are also testing by other metrics such as CPA.