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How does Acast measure podcast download data? (IAB 2.1)
How does Acast measure podcast download data? (IAB 2.1)

How Acast measures your show's audience

Updated over a week ago

Acast takes measurement seriously. We’re fully IAB 2.1 certified, the industry standard for podcast download filtering defined by the Interactive Advertising Bureau (IAB).

How does Acast measure podcast download data?

In order to accurately measure podcast download data, there are some additional steps that need to be taken from the point when Acast receives download data from a platform or app, to when the data can be show in your show's Insights dashboard.

Acast receives a lot of raw download data from these platforms and apps that needs to be filtered and processed to ensure it is accurate. The filters we use are an industry standard, meaning everyone is expected to do it the same way across podcasting.

As podcast download filtering takes a lot of processing, this happens in the Acast system on a daily basis. This is why your shows download data for Today and the Total overview are separate, as today's real-time data is an estimate based on some initial filtering and processing.

How does Acast filter podcast download data?

The industry standard for podcast download filtering is defined by the Interactive Advertising Bureau (IAB) which is an organisation used for standardising measurement across a range of mediums, such as audio and video. Acast is official certified in the 2.1 version of this standard, which is the most up-to-date.

If you want to understand the technical details of podcast download filtering more, there are four key steps in the process:

1. Minimum download length

In order for a download to be counted in your Insights dashboard, at least 60 seconds of the episode needs to be downloaded by the listener.

We calculate this by looking at the total size of the episode audio file, and checking the size of the download. This is measured in a file size unit called 'bytes'.

2. User Agent filtering

A user agent is a piece of raw data sent to Acast that let's us know which app or platform the download happened on. This is what allows us to show you the platform and app download data on the podcast player tab in the Insights dashboard.

In the filtering process, we also need to remove any downloads from user agents - platforms or apps - that are invalid or suspicious, to be able to show you accurate download data. For instance, a 'web crawler' is an app that automatic downloads things such as podcast episode files, without being specifically select by a human.

We use an industry standard list of user agents to check whether a user agent is invalid or suspicious. The list is called the IAB/ABC International Spider & Bots List.

3. IP address filtering

An IP address is a piece of raw data sent to Acast which means we can figure out where in the world a download is happening. An IP address is assigned to a specific location, and this is what allows us to show you the where downloads of your show are happening in the location tab of the Insights dashboard.

Acast also filters the download data to check for any invalid of suspicious IP addresses. For instance, we remove download spam sources that might be download your episodes multiple times without any human listening to them.

Acast uses a database called the TAG Data Center IP list to check to see if an IP address is valid.

4. 24 hour listen limit

Acast filters podcast download data to ensure we only count 1 download per listener per episode within a 24 hour timeframe.

The best way to use the raw data to figure out who is a 'listener' is by using a combination of the location data (IP address) and platform data (user agent). In a 24 hour window, it is industry standard to count a unique combination of these two pieces of data as a 'listener'.

In practice, this means if we can see from the data the spot where a listen was started and on which individual app, we can be confident that this is an individual person and not a group of people.

So, Acast filter downloads so that we only count when listener downloads a specific episode once a day. This process is referred to as 'windowing' and is a requirement of the Interactive Advertising Bureau podcast download standards.

Here's an example of how this all works in practice:

A listener downloads the latest episode of The Intelligence by The Economist. Since the listener downloaded more than 60 seconds of the episode, and they are using a normal podcast app at home, their download is counted as a valid listen under IAB 2.1. However, if the user deletes the episode and re-downloads it later that day, only the first listen is counted.

If you’d like to immerse yourself in all the technical details, you can review the full specifications on our IAB Certificate.

Podcast download data measurement: Frequently Asked Questions (FAQ)

How does Acast measure ad delivery?

The way that Acast measures podcast data, meaning how many downloads your show gets, also informs how we measure ad delivery. You can read in more detail about monetisation and measuring ad delivery here.

How does Acast measure listens from Apple Watch?

According to the industry standard guidelines (IAB 2.1), Acast is required to filter out downloads from Apple Watch as not valid downloads. As we are IAB 2.1 certified, we follow these processes.

It was seen that, once someone listens to an episode using an Apple Watch, the episode is also downloaded on the phone connected to the watch. As the two devices have different device identifiers, they appear to come across as two individually separate downloads. However, it's all the action from one single person. It's an issue that was identified, and IAB requires that we filter these extra downloads out.

Do I need to worry about other wearable technology ?

This has been identified as very specific behaviour with Apple Watches. However, Acast maintains strict compliance with IAB guidelines and standards, and will update our podcasters should any other filters be required.

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