cambiar select option con javascript

<select name="list" id="poblacion">
<option value="11">Person1</option>
<option value="27">Person2</option>
<option value="17">Person3</option>
<option value="10">Person4</option>
<option value="7">Person5</option>
<option value="32">Person6</option>
<option value="18">Person7</option>
<option value="29">Person8</option>
<option value="28">Person9</option>
<option value="34">Person10</option>
<option value="12">Person11</option>
<option value="19">Person12</option>
</select>



 document.getElementById('poblacion').value='Person8';




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