Domain / Page Authority - logarithmic

[eatyourveggies]

SEOmoz says their Domain / Page Authority is logarithmic, meaning that lower rankings are easier to get, higher rankings harder to get.

Makes sense.

But does anyone know what logarithmic equation they use? I'm using the domain and page authority as one metric in amongst other metrics in my keyword analysis. I can't have some metrics linear, others exponential and the SEOmoz one logarithmic.

[ggpaul562]

Hi, any update on this thread? I'm facing the same dilemma currently. I need to know exactly how much more powerful a DA of 50 is vs. 30, for example. If there's any way to access the most top-level estimation of the logarithmic scale, it would be greatly appreciated.

[eatyourveggies]

I received a response in the developers forum which basically said the input data is scaled logarithmically rather than the output being linear which is then scaled logarithmically.

This means it's impossible to answer the question.

However I have asked (and repeated the question here for the sake of anyonewho's interested)...

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What is the distribution of DA values across all values? It would be nice to know that "the median DA across all sites in our database is x." That would at least put the numbers in some perspective - and it's perspective I'm trying to get.

Can you also confirm if the "keyword difficulty" is also calculated with logarithmic inputs? And what's the median keyword difficulty?

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[Dr-Pete]

Unfortunately, I'm not sure it's as simple as an equation - we use a machine-learning algorithm and I think the result just happens to be logarithmic. I know who knows the answer, though, so let me ask and see if it's something we're able to discuss.

[RyanKent]

I understand Adam. As I shared, I am not sure SEOmoz is willing to publicly disclose details of it's algorithm. The best chance to find out more is likely to follow Megan's advice and open a discussion in the developer forum.

[eatyourveggies]

No, I'm not seeking something deeper at all.

I don't care how they work out DA / PA.

The result is between 0 and 100, but they say it's logarithmic.

So is it log(x), or log(x+3), or log2(x)... ? ?

[RyanKent]

I expect you will receive a response from the Moz team by Monday on your other open Q&A / ticket. The person who answers that question may be able to answer this one, or pass your inquiry along to someone who does.

I believe reverse-engineering the PA / DA is pretty straight forward. To the best of my knowledge, the following is true regarding the calculation:

• It is 100% based solely on link data

• OSE is the single data source for the calculation

• there are only a few factors: the PA/DA of any linking pages/sites, the number of links on the page providing the link, the number of links being received by the page/site.

• typical factors known to be used in PR such as relevancy, link location, etc. are not factors in PA/DA

• spam factors are not considered in PA/DA

To the best of my knowledge the above is correct. Only a SEOmoz employee could possibly confirm and I am unsure on their NDA requirements. I would expect their formula is proprietary.

With the above understood, a DA of 30 represents the number and quality of links received for the website. The same applies to PA.

A site with DA of 29: http://www.cheshirecatnarrowboats.co.uk/

A page with PA of 31 http://www.shmoop.com/alice-in-wonderland-looking-glass/cheshire-cat.html

I recognize you are likely aware of the above information and seeking something deeper. I am sharing this information in case it is helpful.

[eatyourveggies]

I absolutely agree to re-invent the wheel is inefficient when people like SEOmoz have thousands of man-hours in developing great metrics... but I use the SEOmoz metrics along side other metrics for a few reasons:

1. To confirm the validity of metrics between providers and my own research

2. To customise the kinds of reports I give clients. For example, sometimes a link profile report is more relevant for a customer than a domain authority report. Sometimes both are relevant, etc.

It just sucks when you have to put caveats on data such as saying that the SEOmoz authority metric is logarithmic but to an unknown logarithmic curve.

I think SEOmoz should publish the logarithmic calculation. I'm not asking for their intellectual property on how they calculate authority or keyword difficulty, etc... I just want to know the logarithmic calculation. Otherwise I'm left asking, "what does 30 actually mean?" In addition, is the keyword difficulty logarithmic? SEOmoz doesn't say.

Adam

[RyanKent]

I can't say exactly what formula is used for PA/DA, but it is designed to emulate PR. Either way, as long as you include PR you already have a logarithmic metric.

Whatever system you use will be challenging. Why?

• Google includes 200+ metrics to determine search result positioning

• Google adjusts search results based on numerous personal factors including location, browsing history, etc

• It is pretty safe to say Google's algorithm includes metrics which are linear, exponential and logarithmic

With dozens of various tools on the market designed to analyze keywords, why not chose to utilize an existing tool which is professionally developed and maintained for this purpose?