Show an Input Field Based On Selected Dropdown And Change a Hidden Input Value Based on That Showed Input Content (if empty and if not empty) // Demo: http://jsfiddle.net/tfntj5ds/

index.css

#ref {
    display:none;
}

index.html

<select id="drop">
    <option>-- Please select --</option>
    <option>Agent / Employer</option>
    <option id="drop_option">Job Seeker</option>
</select>
<br/>
<input name="referral" type="text" placeholder="Referral" id="ref" />
<br/>
<input name="check" value="false" type="text" />

index.js

$('#drop').change(function () {
    var selectedId = $('option:selected', this).attr('id');

    if (selectedId == "drop_option") {
        $('#ref').show("slow", "swing");
        $("#ref").blur(function () {
            if ($(this).val() === "") {
                $('input[name=check]').val('false');
            } else {
                $('input[name=check]').val('true');
            }
        });
    } else {
        $('#ref').hide("slow", "swing");
        $('input[name=check]').val('false');
    }
});