select specific node using xpath

I have a specific node that I want to select using xpath, and it is one of a couple of sibling nodes that has a specific child node... How can I select that using xpath? Here is a mock xml node structure that I wipped up real quick...

 <Templates>
     <TemplateData>
        <Patient>
            <dateOfBirth>1990-09-09T04:00:00Z</dateOfBirth>
            <gender>F</gender>
            <name>
                <firstName>Sam</firstName>
                <lastName>Hill</lastName>
            </name&g开发者_如何学Ct;
            <compositeID>
                <id>102</id>
                <idType>patientID</idType>
            </compositeID>
            <compositeID>
                <id>182</id>
                <idType>populationPatientID</idType>
            </compositeID>
        </Patient>
     </TemplateData>
 </Templates>

Imagine I wanted just one of the compositeID. One who' IdType was populationPatientID... How would I do that?

I thought I would try /Templates/Patient/compositeID[./idType='populationPatientID']/id

But I am really not sure... I definitely need to learn more xpath.