AngularJS - Binding radio buttons to models with boolean values

The correct approach in Angularjs is to use ng-value for non-string values of models.

Modify your code like this:

<label data-ng-repeat="choice in question.choices">
  <input type="radio" name="response" data-ng-model="choice.isUserAnswer" data-ng-value="true" />
  {{choice.text}}
</label>

Ref: Straight from the horse's mouth

That's an odd approach with isUserAnswer. Are you really going to send all three choices back to the server where it will loop through each one checking for isUserAnswer == true? If so, you can try this:

http://jsfiddle.net/hgxjv/4/

HTML:

<input type="radio" name="response" value="true" ng-click="setChoiceForQuestion(question1, choice)"/>

JavaScript:

$scope.setChoiceForQuestion = function (q, c) {
    angular.forEach(q.choices, function (c) {
        c.isUserAnswer = false;
    });

    c.isUserAnswer = true;
};

Alternatively, I'd recommend changing your tack:

http://jsfiddle.net/hgxjv/5/

<input type="radio" name="response" value="{{choice.id}}" ng-model="question1.userChoiceId"/>

That way you can just send {{question1.userChoiceId}} back to the server.