2021 Backlink Survey: Methods, Metrics and Views

Backlinks fascinate some people, delight others and frustrate still others.

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The curious want to know how backlinks are built because the process seems mysterious.

Those who take a calmer view want to know how to work at a relaxed pace because the results come slowly.

Those who love backlinks believe a website takes off as soon as links are built.

Those who hate them see no effect no matter what they do.

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Today, let us uncover one of SEO's most mysterious practices: link building. The historical statistics below come from Aira's 2021 State of Link Building report, a self-reported survey of 253 people across 36 countries. Most questions were optional and some used branching logic, so the percentages describe respondent views and practices rather than causal ranking tests.

1. What Is a Backlink?

As the name suggests, a backlink is a link from another website to yours. A reader can click it to reach your site.

2. Are Backlinks Important?

Yes, they are important.

You can picture a backlink as a vote: a vote from a respected, relevant source may make your site more credible to a search engine and help establish expertise in the field. This is an analogy, not a literal account of every signal in Google's ranking systems.

3. Which Link-Building Methods and Tools Were Common?

3.1 Link-Building Methods in the Survey

The most widely used method was creating links through content marketing; 76% of respondents said they used it.

Another 54% analyzed competitors' backlinks.

Half of respondents used brand-mention reclamation as a link-building tactic.

Guest posting fell from 51% in 2020 to 42% in 2021, a nine-point decline. I took that as a sign that experienced practitioners had encountered problems and were moving away from the tactic, although the survey itself did not establish why use declined.

Paid-link use was reported by 27% of respondents, unchanged from the previous year.

The full set of results is shown below.

Rank	Method	Respondents
1	Content-led link building	76%
2	Competitor backlink analysis	54%
3	Brand mentions	50%
4	HARO	49%
5	Broken-link building	44%
6	Guest posting	42%
7	Newsjacking	34%
8	Resource pages	33%
9	Link-intersect analysis	31%
10	Expert reviews	29%
11	Influencer outreach for links	27%
12	Paid links	27%
13	Directory submissions	24%
14	Skyscraper technique	24%
15	Press-release syndication	19%
16	Article syndication	18%
17	Link exchanges	17%
18	Products or services exchanged for links	15%
19	Image backlink building	13%
20	Podcast links	12%
21	Private blog networks	7%
22	301 redirects	6%
23	Other	3%

Many other tactics exist, but the table covers the mainstream methods listed in the source; each percentage is the share of respondents who selected that method. Link building is one of SEO's hardest disciplines because it demands flexibility.

3.2 Common Link-Building Tools

Different link-building strategies call for different tools.

For finding competitors' links, I preferred Ahrefs. At the time, I described its crawler activity as second only to Google's; that was a historical product claim, not a current independent measurement.

Link retrieval was therefore one of its strengths. The survey results are below.

Rank	Tool	Respondents
1	Ahrefs	81%
2	Google Sheets	55%
3	Semrush	48%
4	Moz	43%
5	HARO	38%
6	BuzzStream	35%
7	Screaming Frog	35%
8	Majestic	33%
9	BuzzSumo	30%
10	Gorkana	11%
11	SparkToro	8%
12	Vuelio	8%
13	Pitchbox	6%
14	Link Research Tools	4%
15	Meltwater	3%
16	CognitiveSEO	3%
17	Kerboo	3%
18	NinjaOutreach	2%
19	Citation Labs Link Prospector	2%
20	Other	5%

For combined link-quality and link-quantity data, respondents trusted Ahrefs more than Google Search Console.

4. Link Measurement and Reporting Standards

How did practitioners measure and report their link-building activity?

This part of the survey focused on the metrics people used and the KPIs by which they assessed their work. About 61% used Ahrefs Domain Rating, and 49% used Moz Domain Authority.

4.1 If You Could Choose One Authority or Quality Measure, Which Would It Be?

Ahrefs and Moz remained the leading choices.

4.2 Which KPIs Were Used to Measure Link Effectiveness?

Rankings were selected by 53% of respondents, and 40% selected the number of linking domains. The original report identifies the second KPI as linking-domain volume, not traffic from those domains.

4.3 Do Brand Mentions Affect Organic Rankings?

More than 74% of respondents believed they did; the remaining 26% did not.

I believed that brand mentions did affect rankings.

In my view, Google valued branding, and a sufficiently strong brand signal could help a site attract more traffic in relevant subject areas. That was my interpretation, not a causal result measured by the survey.

4.4 The Perceived Effect of Links on Organic Results

The survey asked practitioners to rate, on a ten-point scale, how links affected current or future organic rankings.

In the source's summary, 21% believed links had a very strong effect on rankings and another 62% believed they had an effect. I believed backlinks remained very important: content without links could struggle to gain visibility; links without useful content could not create meaningful traffic value. Those are practitioner views, not proof that links alone cause a ranking outcome.

4.5 Will Links Still Be a Google Ranking Signal in Five Years?

In the 2021 survey, 85% believed Google would still use links as a ranking signal five years later.

4.6 Will Links Still Be a Google Ranking Signal in Ten Years?

Another 64% believed links would still be a ranking signal ten years later. I agreed but acknowledged that nobody could know what the internet would look like a decade later. We would have to wait and see.

4.7 How Long Before Link Building Shows an Effect?

The question assumed that Google had not penalized the site and that the site had no major SEO problems. Under those conditions, 51% of respondents selected one to three months.

I thought link quality was the deciding factor and that three months could be enough for strong links. That was my estimate, not a guaranteed timeframe.

4.8 Can Buying Links Improve Rankings?

About 63% of respondents believed it could. I also believed paid links could move rankings and warned that inexperienced buyers were easily misled. That historical belief does not make the practice compliant: Google's current spam policies classify buying or selling links for ranking purposes as link spam, and paid placements must be qualified appropriately.

4.9 Which Factors Matter When Judging Link Relevance?

Topic or page relevance was selected by 55% of respondents, and 52% selected domain relevance.

My own preference was domain relevance because a site devoted to a related subject appeared to offer the strongest topical match. That was my judgment, not a universal rule.

4.10 Do Links Help an Individual Page or the Whole Site More?

Responses were nearly even: 51% selected an individual page and 49% selected the whole site.

I had tested this question myself. In that test, links to an individual page appeared sufficient for a low-difficulty keyword. A harder keyword appeared to require stronger site-wide authority. This was an anecdotal test, not a general causal rule.

4.11 Which Link Attribute Was Believed to Affect Rankings Most?

This was the question many readers wanted answered. The survey found that 71% considered a link from a relevant website the strongest attribute; high authority ranked only third.

My practical shorthand was to perform better than the competitors on the measures that mattered. It was not a universal threshold or guarantee.

5. Content-Led Link Building

At the time, building links through content was the most popular method, so the survey examined it in more detail.

5.1 Do You Produce Content to Generate Links?

Some 89% of respondents said they produced content with the goal of generating links.

5.2 How Many Links Can One Content Campaign Generate?

Within the preceding 12 months, 60% had run a campaign that generated one to nine links, and 56% had run one that generated ten to nineteen. Respondents could select every range they had achieved, so these percentages were not mutually exclusive.

I generally treated more than ten links as a successful campaign. The report's separate success-threshold question was more precise: 33% selected ten to nineteen links, and 61% selected a range between one and nineteen.

5.3 Which Content Formats Were Most Likely to Earn Links?

Long-form, report-style content led with 57%, followed by interactive content at 41% and blog posts at 35%.

6. Link Building for Ecommerce

Many of my readers worked in ecommerce, so this part of the report was especially relevant to them. Aira showed these questions only to the 21% of respondents who identified as ecommerce and explicitly warned that the sample was small.

6.1 What Was the Hardest Part of Ecommerce Link Building?

Scaling links across many product and category pages was selected by 69%. Another 31% selected obtaining topically relevant links.

6.2 Which Ecommerce Pages Did Teams Target Most Actively?

Category pages and pages within a topic cluster each received 38%.

If I wanted links to look natural, I would target an article and then use internal linking as a middleman to support a commercial page.

6.3 Did Teams Give Away Products During Link Building?

Some 63% said they did not give products away, and 38% said they did; the one-point excess comes from rounded survey percentages.

I would give a product for an independent review and leave the decision to link to the blogger. Even then, a free product supplied in return for a review containing a link can fall within Google's link-spam examples unless the commercial relationship is qualified appropriately.

Final Thoughts

SEO depends on detail. It does not suit rushed or careless work, and link building is especially demanding.

I saw that difficulty as one of the natural barriers Google creates.

The same barrier gives smaller operators a low-cost opportunity to improve their position. The source then invited dissatisfied readers to learn SEO through its WeChat account; that China-only CTA and its QR image are not carried into this global English page.