validation using conditional statement

validation using conditional statement

I have the following code:
      <select name="selCompletedBy" id="selCompletedBy">
       <option value="Dr">Dr</option>
       <option value="Nurse">Nurse</option>
       <option value="Therapist">Therapist</option>
       <option value="Psychologist">Psychologist</option>
       <option value="Other">Other</option>
      </select>
       






<input type="text" name="completedOther" id="completedOther" size="45" maxlength="50" validate="required:true" >
 
Then in the validation :
    completedOther: {   required: "#selCompletedBy.selectedvalue=='Other'"     }
 
But this causes an error. How do i make the completedOther text field required if the selCompletedBy = 'Other'
 
Thanks