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)...

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?

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)... ? ?

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

Many sites will have "Modified Since Http Header" enabled. If so, then when looking at a page you want to check, type this into your address bar:

javascript:alert(document.lastModified)

But that won't work on all sites as some may disallow javascript execution in that manner. But also if it's a dynamic site and the web owner hasn't configured their Modified Since Http Header properly, then you'll get incorrect dates anyway.

You can see if a website has the Modified Since Http Header enabled:

http://www.hscripts.com/tools/if-modified-since/index.php

You can use the internet archive to look at previous versions of a website (unless they've disallowed this in the .htaccess):

http://archive.org/index.php

A cool tool I use to alert me to when a competitor (or any website) content is updated is:

http://www.changedetection.com

Enjoy

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.