Check "Select all" checkbox onload using Knockout

I have a set of Checkboxes and a Select All checkbox implemented in the following way using Knockout. I need the "Select All" checkbox to be checked by default on page load.

$(document).ready(function(){
    viewModel=new model(ko,$);
    ko.applyBindings(viewModel);
});

function model(ko,$){
     var jsonResponse= $.parseJSON(response);

     this.factors=ko.observableArray(jsonResponse["factors"]);
    this.selectedFactors=ko.observableArray();

     this.selectAll = ko.dependentObservable({
        read: function() {
            return this.selectedFactors().length === this.factors().length;
        },
        write: function(newValue) {
            this.selectedFactors(this.selectedFactors().length === this.factors().length ? [] : this.factors().slice(0));
        },
        owner: this 
    });

}

HTML:

<table>
    <tr>
        <td><input type="checkbox" id="selectAll" data-bind="checked: selectAll" />Select All</td>
   </tr>
</table>
<table data-bind="foreach: factorsSplitJsonArray">
    <tr data-bind="foreach: $data">
        <td>
            <!-- ko if: $data.hasOwnProperty("factorCode") -->
            <input type="checkbox" class="jqFactors" id="jqFactors" data-bind="checkedValue: $data, checked: $root.selectedFactors" /> 
            <span data-bind="text: factorDescription"></span> 
            <!-- /ko -->
        </td>
    </tr>
</table>

When I select or deselect any checkbox or the SelectAll checkbox the observableArray ie selectedFactors get changed. Now I need the "Select All" checkbox to be selected by default on page load and the selectedFactors should also have all the selected factors in it.

I am new to Knockout and unable to find out how to implement this using Knockout. What if we somehow call the function selectAll explicitly, will it do the job? How do I call a ko.dependentObservable function. Can some one please help me.