<story><title>The 50 million dollar lie</title><url>http://garyrubinstein.teachforus.org/2013/01/09/the-50-million-dollar-lie/</url></story><parent_chain><item><author>kenjackson</author><text>This is a surprising blog post in that I draw the complete opposite conclusion the author does.  The author seems to think that the averaging hides volatility (which it does), which leads to incorrect conclusions drawn.  Whereas to me it looks like it removes visual noise to show an actual trend.&lt;p&gt;In his original scatter plot, because of the big ball in the middle it&apos;s easy to handwave and say, &quot;look a random blob&quot; -- but even a slightly longer look seems to indicate there is a positive correlation in the data.  His averaging that he does at the end, IMO, makes it clear.</text></item></parent_chain><comment><author>pdonis</author><text>You&apos;re missing the point. The author agreed that there is a slight positive correlation in the data. But the averaging makes it look like there is a &lt;i&gt;strong&lt;/i&gt; positive correlation in the data, which there isn&apos;t.&lt;p&gt;In other words: without the averaging, you are seeing the full implications of the data: slight positive correlation, but a lot of scatter--i.e., not much meat there. With the averaging, you are seeing &lt;i&gt;only&lt;/i&gt; the positive correlation, with all other information filtered out--i.e., you are seeing only part of the picture, and it&apos;s the part that, surprise, surprise, makes the person who ordered the data collected look good.</text></comment>
<story><title>The 50 million dollar lie</title><url>http://garyrubinstein.teachforus.org/2013/01/09/the-50-million-dollar-lie/</url></story><parent_chain><item><author>kenjackson</author><text>This is a surprising blog post in that I draw the complete opposite conclusion the author does.  The author seems to think that the averaging hides volatility (which it does), which leads to incorrect conclusions drawn.  Whereas to me it looks like it removes visual noise to show an actual trend.&lt;p&gt;In his original scatter plot, because of the big ball in the middle it&apos;s easy to handwave and say, &quot;look a random blob&quot; -- but even a slightly longer look seems to indicate there is a positive correlation in the data.  His averaging that he does at the end, IMO, makes it clear.</text></item></parent_chain><comment><author>Alex3917</author><text>&quot;Whereas to me it looks like it removes visual noise to show an actual trend.&quot;&lt;p&gt;Except for that in this case the noise is more important than the trend. Think about it, if you&apos;re firing or sanctioning perhaps 30%+ of teachers each year for no reason, then only complete morons would go into teaching.&lt;p&gt;It&apos;s the same as airport security, where a .1% false positive rate is unacceptable, whereas a 75% false negative rate is just fine.</text></comment>