React.js generate new random number

I'm trying to create a new random number which will be set as state after a method. It works perfectly on refresh, but I can't 'generate' a new number after the button click.

Here's my code at the moment:

var QuizContainer = React.createClass({

  randomNumber: function(){
    return Math.floor((Math.random() * Data.length) + 0);
  },

  getInitialState: function(){
    var rand = this.randomNumber();
    return {
      answerList: Data[rand].answer,
      answerQuestion: Data[rand].question,
      correctAnswer: Data[rand].correct,
      score: 0,
      timer: 30
    }
  }, 

  success: function(){
    this.setState({score: this.state.score + 1})
  },

  fail: function(){
    this.setState({score: 0})
    this.getInitialState();
  },

  handleClick: function(child){
    child.props.singleAnswer == this.state.correctAnswer ? this.success() : this.fail()
  },

  render: function(){
    return(
      <div>
        <Timer timer={this.state.timer} />
        <Score currentScore={this.state.score} />
        <QuestionContainer answerQuestion={this.state.answerQuestion} />
        <ButtonContainer onClick={this.handleClick} correctAnswer={this.state.correctAnswer} answerList={this.state.answerList} />
      </div>
    )
  }

})

module.exports = QuizContainer;

If anyone's able to help I'd be very grateful! Thanks!