Unable to set checked as a default - knockout checkbox

I'm new in knockout and I couldn't solve a little problem, which is to set a checkbox as a default selected.

HTML:

<tr>
    <td>
        <input id="summary" type="checkbox" checked="checked" data-bind="checked: Summarise"/> 
        Summary 
    </td>
</tr>

Doc.Ready:

if (!viewModel) {
    viewModel = new ViewModel();
}

ko.applyBindings(viewModel, document.getElementById("ParametersView"));

This returns unchecked checkbox when it gets called.