Why does my character jump at varying heights when the jump button is pressed?

Hey, does anyone know why this code is causing my character to jump at varying heights? It isn’t proportional to how long the button is held and seems random.

using UnityEngine;
using System.Collections;

public class DodgeManController : MonoBehaviour {
public float maxSpeed = 10.0f;
public float jumpForce = 5.0f;
bool grounded;
public float groundRadius = 0.2f;
public Transform groundCheck;
public LayerMask whatIsGround;

// Use this for initialization
void Start () {

}

// Update is called once per frame
void Update(){
	if (grounded && Input.GetAxis ("Jump") > 0) {
		rigidbody2D.AddForce (Vector2.up * jumpForce,ForceMode2D.Impulse);
	}
}

void FixedUpdate () {

	grounded = Physics2D.OverlapCircle (groundCheck.position, groundRadius, whatIsGround);

	float move = Input.GetAxis ("Horizontal");

	rigidbody2D.velocity = new Vector2 (move * maxSpeed, rigidbody2D.velocity.y);

}

}

Answered here Character jumping at random heights. What in my code is causing this? - Unity Answers