(1) Any attribute, phenomenon or event that can have different qualitative or quantitative values. Typically, a form of metadata goes with the variable, there is a variable definition that describes what is varying and there is a value for the variable. Variables are typically assessed in a clinical trial.
When you click a link for an email address or website, your Mac opens the app you've set for that kind of link. Mail is the default email app and Safari is the default web browser on your Mac. If you install other email apps or web browsers, you might want to set them to open when you click an email link or web link. Open the Mail app.
The best way to see the sites. The best browser for your Mac is the one that comes with your Mac. Safari is faster and more energy efficient than other browsers, so sites are more responsive and your notebook battery lasts longer between charges. Built-in privacy features help keep your browsing your business.