why we have to give the var a false statment?what this is for?

var education = "no high school diploma"
var salary = 0;

switch (education) {
  case "no high school diploma":
    salary = "25,636";
    break;
  case "a high school diploma":
    salary = "35,256";
    break;
  case "an Associate's degree":
    salary = "41,496";
    break;
  case "a Bachelor's degree":
    salary = "59,124";
    break;
  case "a Master's degree":
    salary = "69,732";
    break;
  case "a Professional degree":
    salary = "89,960";
    break;
  case "a Doctoral degree":
    salary = "84,396";
}

console.log("In 2015, a person with " + education + " earned an average of $" + salary + "/year.");