Angular 2 radio button first always selected even when I need it not to be
<p>I'm using angular 2 material radio button and a function with attribute [checked] to determine if radio button should be checked or not:</p>

<pre><code>&lt;md-radio-group class="th-modal-radio-group"&gt;
                    &lt;md-radio-button
                            value="estimated" class="th-modal-radio-btn"
                            [checked]="isChecked('estimated')"&gt;Estimated
                    &lt;/md-radio-button&gt;
                    &lt;md-radio-button
                            value="contractual" class="th-modal-radio-btn"
                            [checked]="isChecked('contractual')"&gt;Contractual
                    &lt;/md-radio-button&gt;
                    &lt;md-radio-button
                            value="completed" class="th-modal-radio-btn"
                            [checked]="isChecked('completed')"&gt;Completed
                        &lt;/md-radio-button&gt;
&lt;/md-radio-group&gt;
</code></pre>

<p>The<code>isChecked()</code>function is working correctly but even when it returns <code>false</code>on first radio button it appears as default selection. I need that first radio button to be checked ONLY when isChecked returns true</p>