Bounce Rate Question - The percent calculated does not add up

[DaveGuyMan]

Hello All,

I'm attempting to see why organic search bounce rate has increased by 5% when compared to last year for a certain section of my website. I am using a custom segment to filter the specific pages I want to look at. Once the custom segment is set, I go to Acquisition - > Channels - > Organic. Then, I click the Landing Pages tab. Because we don't have keyword data anymore the only thing I can look at is the landing pages that contributed to the change in bounce. Finally, I set my date range and compare to the same date range as last year. Once I set the date range I am presented with a list of URLs and the percent change in bounce rate for each URL. This is where I get confused. If you look at the average bounce rate at the top of the column (example 1 attached) it does not add up with the data below it. If you export all of the data to excel, and then do an "Average" function in Excel, the data adds up to 17.29% instead of 35.04% for Sept. 2013. Why does this not add up? Isn't GA calculating the Average?

Also, I always notice several URLs with only 1 session per URL. Several of these 1 session URLs have a 100% bounce rate. Since the bounce rate at the top of the column (example1) is a reflection of the average bounce rate, wouldn't these 1 session URLs significantly distort my data?

I ultimately just want to see the pages that are contributing to the increased bounce rate when compared to last year. Having a hard time figuring this one out.

Thank you all,

Dave

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[DaveGuyMan]

Andy, Thank you so much. I had a feeling I was making this out to be something much harder than it actually was. Of course you can't average percentages. That explains everything. Thank you!

[Andy-Halliday]

If I am reading the question correctly, then its more of a maths questions rather than an SEO question.

You simply can't average % as some figures have more weighting than others, pages with more page views will have a higher weighting to the total average %, than the pages with 1 page view and 100% bounce rate. So simply using the average formula in Excel wouldn't take into account the weighting and assume they all have equal weighting (which unless ever page had the exact same number of page views, isn't the case).

Here is probably a better explanation: http://www.ehow.co.uk/how_6437936_calculate-averages-percentages.html

Hope this is useful.

Thanks

Andy