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200 lines
6.7 KiB
Markdown
200 lines
6.7 KiB
Markdown
---
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title: How to set up A/B tests in PHP
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date: 2024-02-08
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author:
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- lior-neu-ner
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tags:
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- experimentation
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---
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import { ProductScreenshot } from 'components/ProductScreenshot'
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export const EventsInPostHogLight = "https://res.cloudinary.com/dmukukwp6/image/upload/posthog.com/contents/images/tutorials/php-ab-tests/events-light.png"
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export const EventsInPostHogDark = "https://res.cloudinary.com/dmukukwp6/image/upload/posthog.com/contents/images/tutorials/php-ab-tests/events-dark.png"
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export const ResultsLight = "https://res.cloudinary.com/dmukukwp6/image/upload/posthog.com/contents/images/tutorials/php-ab-tests/results-light.png"
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export const ResultsDark = "https://res.cloudinary.com/dmukukwp6/image/upload/posthog.com/contents/images/tutorials/php-ab-tests/results-dark.png"
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A/B tests help you improve your PHP app by enabling you to compare the impact of changes on key metrics. To show you how to set one up, we create a basic PHP app, add PostHog, create an A/B test, and implement the code for it.
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## 1. Create a basic PHP app
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First, ensure [PHP](https://www.php.net/manual/en/install.php) is installed. Then, create a new folder for your project called `php-ab-tests`. In this folder, create an `index.php` file:
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```bash
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mkdir php-ab-tests
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cd ./php-ab-tests
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touch index.php
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```
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Next, add the following code to `index.php` to set up a basic page with a heading and paragraph:
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```php file=index.php
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<?php
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$paragraphText = 'Placeholder text';
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?>
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<!DOCTYPE html>
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<html>
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<body>
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<h1>PHP A/B Testing Tutorial</h1>
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<p><?php echo $paragraphText; ?></p>
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</body>
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</html>
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```
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Run `php -S localhost:8000` and navigate to `http://localhost:8000` to see our app in action.
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## 2. Add PostHog to your app
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With our app set up, it’s time to install and set up PostHog. If you don't have a PostHog instance, you can [sign up for free](https://us.posthog.com/signup).
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To start, make sure [Composer](https://getcomposer.org/) is installed. Then run `composer require posthog/posthog-php` to install [PostHog’s PHP SDK](/docs/libraries/php).
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Then, initialize PostHog at the top of `index.php` using your project API key and instance address (you can find these in [your project settings](https://us.posthog.com/project/settings)):
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```php file=index.php
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<?php
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require_once __DIR__ . '/vendor/autoload.php';
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use PostHog\PostHog;
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PostHog::init(
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'<ph_project_api_key>',
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['host' => '<ph_client_api_host>']
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);
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// rest of your code
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```
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Lastly, we [capture](/docs/product-analytics/capture-events) a `$pageview` event using `PostHog::capture()`:
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```php file=index.php
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<?php
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require_once __DIR__ . '/vendor/autoload.php';
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use PostHog\PostHog;
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PostHog::init(
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'<ph_project_api_key>',
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['host' => '<ph_client_api_host>']
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);
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$paragraphText = 'Placeholder text';
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$distinctId = 'placeholder-user-id';
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PostHog::capture([
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'distinctId' => $distinctId,
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'event' => '$pageview'
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]);
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?>
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<!-- your existing html code -->
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```
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With this set up, restart your app and then refresh your browser a few times. You should now see the captured event in your [PostHog activity tab](https://us.posthog.com/events).
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<ProductScreenshot
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imageLight={EventsInPostHogLight}
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imageDark={EventsInPostHogDark}
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alt="Events captured in PostHog"
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classes="rounded"
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/>
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## 3. Create an A/B test in PostHog
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Next, go to the [A/B testing tab](https://us.posthog.com/experiments) and create an A/B test by clicking the **New experiment** button. Add the following details to your experiment:
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1. Name it "My cool experiment".
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2. Set "Feature flag key" to `my-cool-experiment`.
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3. Use the default values for all other fields.
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4. Click **Save as draft**.
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<ProductScreenshot
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imageLight="https://res.cloudinary.com/dmukukwp6/image/upload/Clean_Shot_2025_01_16_at_09_53_57_2x_2b998be1a8.png"
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imageDark="https://res.cloudinary.com/dmukukwp6/image/upload/Clean_Shot_2025_01_16_at_09_20_55_2x_4be4106819.png"
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alt="Experiment setup in PostHog"
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classes="rounded"
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/>
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Once created, set the primary metric to a trend of `pageview` and then click **Launch**.
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## 4. Implement the A/B test code
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To implement the A/B test, we:
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1. Fetch the `my-cool-experiment` flag using [`PostHog::getFeatureFlag()`](/docs/libraries/php#feature-flags).
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2. Update the paragraph text based on whether the user is in the `control` or `test` variant of the experiment.
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```php file=index.php
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<?php
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require_once __DIR__ . '/vendor/autoload.php';
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use PostHog\PostHog;
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PostHog::init(
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'<ph_project_api_key>',
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['host' => '<ph_client_api_host>']
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);
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$paragraphText = 'Placeholder text';
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$distinctId = 'placeholder-user-id';
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// fetch the feature flag
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$enabledVariant = PostHog::getFeatureFlag(
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'my-cool-experiment',
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$distinctId
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);
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if ($enabledVariant === "control") {
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$paragraphText = "Control variant!";
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} else if ($enabledVariant === "test") {
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$paragraphText = "Test variant!";
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}
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// rest of your code
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```
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When you restart your app and refresh the page, you should see the text updated to either `Control variant!` or `Test variant!`.
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> **💡 Setting the correct `distinctId`:**
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>
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> You may notice that we set `distinctId = 'placeholder-user-id'` in our flag call above. In production apps, to ensure you fetch the correct flag value for your user, `distinctId` should be set to their unique ID.
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>
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> For logged-in users, you typically use their email or user ID as their `distinctId`. For logged-out users, assuming they made their request from a browser, you can use values from their request cookies. See an example of this in our [Nuxt feature flags tutorial](/tutorials/nuxt-feature-flags#setting-the-correct-distinctid).
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## 5. Include the feature flag when capturing your event
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To ensure our goal metric is correctly calculated for each experiment variant, we need to include our feature flag information when capturing our `$pageview` event.
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To do this, we add the [`$feature/my-cool-experiment`](/docs/libraries/php#step-2-include-feature-flag-information-when-capturing-events) key to our event properties:
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```php file=index.php
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<?php
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// rest of your code
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PostHog::capture([
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'distinctId' => $distinctId,
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'event' => '$pageview',
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'properties' => [
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'$feature/my-cool-experiment' => $enabledVariant
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]
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]);
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// rest of your code
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```
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Now PostHog is able to calculate our goal metric for our experiment results:
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<ProductScreenshot
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imageLight={ResultsLight}
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imageDark={ResultsDark}
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alt="Experiment results in PostHog"
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classes="rounded"
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/>
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## Further reading
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- [A software engineer's guide to A/B testing](/product-engineers/ab-testing-guide-for-engineers)
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- [How to set up feature flags in PHP](/tutorials/php-feature-flags)
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- [How to set up analytics in PHP](/tutorials/php-analytics)
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<NewsletterForm /> |