Google Analytics and the Google Analytics developer platform allows you to collect, configure, and analyze your data to reach the right audience.

Libraries and SDKs for tracking

• Web Tracking (analytics.js): Measure user interaction with websites or web applications.
• Android: Measure user interaction with Android applications.
• iOS: Measure user interaction with iOS applications.
• Measurement Protocol: Measure user interaction in any environment with this low-level protocol.
• Unity: Track user interactions in Unity games.
• AMP HTML: Track user interactions in AMP pages.

APIs for reporting and configuration

• Core Reporting API: Query for dimensions and metrics to produce customized reports.
• Embed API: Easily create and embed dashboards on a 3rd party website in minutes.
• Multi-Channel Funnels Reporting API: Query the traffic source paths that lead to a user's goal conversion.
• Real Time Reporting API: Report on activity occurring on your property right now.
• Metadata API: Access the list of API dimensions and metrics and their attributes.
• Management API: View and manage accounts, properties, views, filters, uploads, permissions, etc.
• Provisioning API: Create Google Analytics accounts and enable Google Analytics for your customers at scale.

Sampling in Analytics is the practice of selecting a subset of data from your traffic and reporting on the trends available in that sample set. Sampling is widely used in statistical analysis because analyzing a subset of data gives similar results to analyzing all of the data. In addition, sampling speeds up processing for reports when the volume of data is so large as to slow down report queries.

In layman's terms this means that when there is a large amount of data we can take a chunk of that data and analyze based upon that sample. When looking at large data sets it can often be faster to analyse upon a sample rather then the full data set. However one must always take into account that the results will not be 100% the same as if you had done the analysis upon the full data set.

Google Analytics handle's sampling is as follows:

Analytics inspects the number of sessions for the specified date range at the property level. If the number of sessions in the property over the given date range exceeds 500k sessions (100M for Analytics 360)1, Analytics will employ a sampling algorithm which uses a sample set proportional to the distribution of sessions by day for the selected date range. Thus, the session sampling rate varies for every query depending on the number of sessions included in the selected date range for the given property.

Additional information can be found here: How sampling works

The example above has two tracking events, Event Tracking and Exception Tracking.

Event Tracking will allow you to see JS errors in real-time. Under Real Time -> Events sections.

Unfortunately, your error messages will be limited by 500 Bytes, so you will not be able to understand a problem properly, however you will know that something is going wrong.

Exception Tracking will give you more detailed report, with full error message and browser information.

You can generate Exception Tracking report with Custom Reports.