_includes/analytics.html

{% if site.analytics.provider and page.analytics != false %}

{% case site.analytics.provider %}
{% when "google" %}
  {% include /analytics-providers/google.html %}
{% when "google-universal" %}
  {% include /analytics-providers/google-universal.html %}
{% when "custom" %}
  {% include /analytics-providers/custom.html %}
{% endcase %}

{% endif %}