# Traffic allocation step

When creating a test or a personalization campaign, you need to define the percentage of visitors assigned to the variation(s) (in case of a test) or scenario(s) (in case of a personalization) and to the original version of your website.

To learn about the traffic allocation step of the campaign creation flow, refer to [Campaign flow: Traffic Allocation step](https://docs.abtasty.com/~/revisions/jp976foDpdJWagLtM22v/web-experimentation-and-personalization/traffic-allocation/campaign-flow-traffic-allocation-step).\\

## Allocation system <a href="#h_01hzpdhrxvnbk48ap7dcnx0ert" id="h_01hzpdhrxvnbk48ap7dcnx0ert"></a>

For each individual visitor, we compute what we call a seed, a unique alphanumeric string that will be persistent in time. This seed, also unique for each campaign, will be used to generate a score between 1 and 100 **and then the same logic as before applies.**

As the seed is computed each time, we do not need to store the result anymore.

This allocation system doesn't work under the HTTP protocol as we are using cryptographic tools that are only available under a secure protocol.

If the tag detects it is on an insecure environment, it will automatically fallback to the old mechanism.

Let's take the example of a 50/50 campaign. If a visitor gets a score of 51, they will be exposed to the variant (a score above 49).

When Even Allocation is active, the platform restricts you from manually setting a variation's traffic allocation to a value exceeding the original allocation.

To know more about this behaviour, read our [Even allocation article](https://docs.abtasty.com/~/revisions/jp976foDpdJWagLtM22v/web-experimentation-and-personalization/traffic-allocation/even-allocation).

If you decide to change the allocation from 10/10 to 50/50, the allocation will be computed again and their score will now place them in the original. **The visitor will switch** **from one variant to another.**

## Allocation behavior <a href="#h_01jayy3f3gh1gxmp5re26nar8y" id="h_01jayy3f3gh1gxmp5re26nar8y"></a>

This table shows the different categories of users, representing your entire website traffic. For each category, information on what the users will see is displayed:

| **🚦 Type of traffic**                                      | **🍪 Visitor’s cookie campaign information (*****ABTasty*****&#x20;cookie)**                                                                                                                              | **💬 Comment**                                                                                                                                |
| ----------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------- |
| 👻 Untracked visitors                                       | <p><strong>campaignId=</strong><em><strong>\[campaignId]</strong></em><br><strong>value=</strong><em><strong>-1</strong></em></p>                                                                         | Visitors who see the original version of your website but whose actions will not be taken into account.                                       |
| 🎯 Tracked visitors (% of unique visitors of your campaign) | <p><strong>campaignId=</strong><em><strong>\[campaignId]</strong></em></p><p><strong>value/variationId=</strong><em><strong>0</strong></em> or <em><strong>variationID</strong></em> of the variation</p> | The original version of your website or a new variation/scenario of your website                                                              |
| 🏛 Traffic allocated to original                            | <p><strong>campaignId=</strong><em><strong>\[campaignId]</strong></em><br><strong>value=</strong><em><strong>0</strong></em></p>                                                                          | Visitors within the test sample who see the original version of your website.                                                                 |
| 🆕 Traffic allocated to variations                          | <p><strong>campaignId=</strong><em><strong>\[campaignId]</strong></em></p><p><strong>variationId=\[</strong><em><strong>variationID</strong></em><strong> of the variation]</strong></p>                  | Visitors within the test sample who see a new version of your website (or one of the new versions if there are several variations/scenarios). |

It is highly not recommended to change the allocation while a campaign is running. Doing so might severely impact the reliability of your results, even more now with the new system. We strongly advise you to duplicate your campaign and start a fresh new one unless you consider the risk is low (the campaign is still in QA, only a few visitors have seen it until now, etc ..).

## Use case <a href="#h_01hvvacead35m5nnc2em1psbkd" id="h_01hvvacead35m5nnc2em1psbkd"></a>

For example, let’s say you’ve implemented a ‘risky’ test and want to limit risk-taking. In this case, you can limit the number of visitors tracked and so that 40% of visitors aren’t tracked. That way, you reduce the test sample and limit the visibility of your new version(s). This means that these 40% of untracked visitors will see the original version of your website but won’t receive a cookie in their browser related to the test. Their actions on the website won’t be tracked unless you decide to increase the percentage of tracked visitors.\
The percentage of visitors that you track depends on the volumetry of your website. For example, if your website has over 10M unique visitors per month, you can choose to track only 20% of the entire traffic (and limit the test sample to 20%). However, if you have around 200k unique visitors per month and decide to track 20% of the traffic, you won’t reach reliability quickly enough to determine whether you can increase the percentage of tracked visitors. For more information, refer to [Campaign reporting](https://docs.abtasty.com/~/revisions/jp976foDpdJWagLtM22v/reporting-and-performances/reporting/campaign-reporting).

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