testing presumably certain form non-null component exists... somewhere

i have xml looks like

<answers>
   <answer>
      <question-number>1</question-number>
      <value>3</value>
      <mean xsi:nil="1" />
    </answer>
   <answer>
      <question-number>2</question-number>
      <value>2</value>
      <mean>2.3</mean>
    </answer>
   <answer>
      <question-number>3</question-number>
      <value>3</value>
      <mean xsi:nil="1" />
    </answer>
....
</answers>

i'm formatting any answer controlling xsl:for-each. there meant donation i have graphical illustration mean. appetite lists answers meant always null.

at bottom page i wish put parable explaining graphical illustration mean. nonetheless i wholly wish seem i indeed displayed meant during all. i wish means check, after shutting xsl:for-each, contend "do any answer elements have non-null meant value?".

really certain that.