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 |  | 
 | <h1 id="test-stats-aggregators">Test Stats Aggregators</h1> | 
 |  | 
 | <p>This Apache Druid (incubating) extension incorporates test statistics related aggregators, including z-score and p-value. Please refer to <a href="https://www.paypal-engineering.com/2017/06/29/democratizing-experimentation-data-for-product-innovations/">https://www.paypal-engineering.com/2017/06/29/democratizing-experimentation-data-for-product-innovations/</a> for math background and details.</p> | 
 |  | 
 | <p>Make sure to include <code>druid-stats</code> extension in order to use these aggregrators.</p> | 
 |  | 
 | <h2 id="z-score-for-two-sample-ztests-post-aggregator">Z-Score for two sample ztests post aggregator</h2> | 
 |  | 
 | <p>Please refer to <a href="https://www.isixsigma.com/tools-templates/hypothesis-testing/making-sense-two-proportions-test/">https://www.isixsigma.com/tools-templates/hypothesis-testing/making-sense-two-proportions-test/</a> and <a href="http://www.ucs.louisiana.edu/%7Ejcb0773/Berry_statbook/Berry_statbook_chpt6.pdf">http://www.ucs.louisiana.edu/~jcb0773/Berry_statbook/Berry_statbook_chpt6.pdf</a> for more details.</p> | 
 |  | 
 | <p>z = (p1 - p2) / S.E.  (assuming null hypothesis is true)</p> | 
 |  | 
 | <p>Please see below for p1 and p2. | 
 | Please note S.E. stands for standard error where </p> | 
 |  | 
 | <p>S.E. = sqrt{ p1 * ( 1 - p1 )/n1 + p2 * (1 - p2)/n2) }</p> | 
 |  | 
 | <p>(p1 – p2) is the observed difference between two sample proportions.</p> | 
 |  | 
 | <h3 id="zscore2sample-post-aggregator">zscore2sample post aggregator</h3> | 
 |  | 
 | <ul> | 
 | <li><strong><code>zscore2sample</code></strong>: calculate the z-score using two-sample z-test while converting binary variables (<strong><em>e.g.</em></strong> success or not) to continuous variables (<strong><em>e.g.</em></strong> conversion rate).</li> | 
 | </ul> | 
 | <div class="highlight"><pre><code class="language-json" data-lang="json"><span></span><span class="p">{</span> | 
 |   <span class="nt">"type"</span><span class="p">:</span> <span class="s2">"zscore2sample"</span><span class="p">,</span> | 
 |   <span class="nt">"name"</span><span class="p">:</span> <span class="s2">"<output_name>"</span><span class="p">,</span> | 
 |   <span class="nt">"successCount1"</span><span class="p">:</span> <span class="err"><post_aggregator></span> <span class="err">success</span> <span class="err">count</span> <span class="err">of</span> <span class="err">sample</span> <span class="mi">1</span><span class="p">,</span> | 
 |   <span class="nt">"sample1Size"</span><span class="p">:</span> <span class="err"><post_aggregaror></span> <span class="err">sample</span> <span class="mi">1</span> <span class="err">size</span><span class="p">,</span> | 
 |   <span class="nt">"successCount2"</span><span class="p">:</span> <span class="err"><post_aggregator></span> <span class="err">success</span> <span class="err">count</span> <span class="err">of</span> <span class="err">sample</span> <span class="mi">2</span><span class="p">,</span> | 
 |   <span class="nt">"sample2Size"</span> <span class="p">:</span> <span class="err"><post_aggregator></span> <span class="err">sample</span> <span class="mi">2</span> <span class="err">size</span> | 
 | <span class="p">}</span> | 
 | </code></pre></div> | 
 | <p>Please note the post aggregator will be converting binary variables to continuous variables for two population proportions.  Specifically</p> | 
 |  | 
 | <p>p1 = (successCount1) / (sample size 1)</p> | 
 |  | 
 | <p>p2 = (successCount2) / (sample size 2)</p> | 
 |  | 
 | <h3 id="pvalue2tailedztest-post-aggregator">pvalue2tailedZtest post aggregator</h3> | 
 |  | 
 | <ul> | 
 | <li><strong><code>pvalue2tailedZtest</code></strong>: calculate p-value of two-sided z-test from zscore | 
 |  | 
 | <ul> | 
 | <li><strong><em>pvalue2tailedZtest(zscore)</em></strong> - the input is a z-score which can be calculated using the zscore2sample post aggregator</li> | 
 | </ul></li> | 
 | </ul> | 
 | <div class="highlight"><pre><code class="language-json" data-lang="json"><span></span><span class="p">{</span> | 
 |   <span class="nt">"type"</span><span class="p">:</span> <span class="s2">"pvalue2tailedZtest"</span><span class="p">,</span> | 
 |   <span class="nt">"name"</span><span class="p">:</span> <span class="s2">"<output_name>"</span><span class="p">,</span> | 
 |   <span class="nt">"zScore"</span><span class="p">:</span> <span class="err"><zscore</span> <span class="err">post_aggregator></span> | 
 | <span class="p">}</span> | 
 | </code></pre></div> | 
 | <h2 id="example-usage">Example Usage</h2> | 
 |  | 
 | <p>In this example, we use zscore2sample post aggregator to calculate z-score, and then feed the z-score to pvalue2tailedZtest post aggregator to calculate p-value.</p> | 
 |  | 
 | <p>A JSON query example can be as follows:</p> | 
 | <div class="highlight"><pre><code class="language-json" data-lang="json"><span></span><span class="p">{</span> | 
 |   <span class="err">...</span> | 
 |     <span class="nt">"postAggregations"</span> <span class="p">:</span> <span class="p">{</span> | 
 |     <span class="nt">"type"</span>   <span class="p">:</span> <span class="s2">"pvalue2tailedZtest"</span><span class="p">,</span> | 
 |     <span class="nt">"name"</span>   <span class="p">:</span> <span class="s2">"pvalue"</span><span class="p">,</span> | 
 |     <span class="nt">"zScore"</span> <span class="p">:</span>  | 
 |     <span class="p">{</span> | 
 |      <span class="nt">"type"</span>   <span class="p">:</span> <span class="s2">"zscore2sample"</span><span class="p">,</span> | 
 |      <span class="nt">"name"</span>   <span class="p">:</span> <span class="s2">"zscore"</span><span class="p">,</span> | 
 |      <span class="nt">"successCount1"</span> <span class="p">:</span> | 
 |        <span class="p">{</span> <span class="nt">"type"</span>   <span class="p">:</span> <span class="s2">"constant"</span><span class="p">,</span> | 
 |          <span class="nt">"name"</span>   <span class="p">:</span> <span class="s2">"successCountFromPopulation1Sample"</span><span class="p">,</span> | 
 |          <span class="nt">"value"</span>  <span class="p">:</span> <span class="mi">300</span> | 
 |        <span class="p">},</span> | 
 |      <span class="nt">"sample1Size"</span> <span class="p">:</span> | 
 |        <span class="p">{</span> <span class="nt">"type"</span>   <span class="p">:</span> <span class="s2">"constant"</span><span class="p">,</span> | 
 |          <span class="nt">"name"</span>   <span class="p">:</span> <span class="s2">"sampleSizeOfPopulation1"</span><span class="p">,</span> | 
 |          <span class="nt">"value"</span>  <span class="p">:</span> <span class="mi">500</span> | 
 |        <span class="p">},</span> | 
 |      <span class="nt">"successCount2"</span><span class="p">:</span> | 
 |        <span class="p">{</span> <span class="nt">"type"</span>   <span class="p">:</span> <span class="s2">"constant"</span><span class="p">,</span> | 
 |          <span class="nt">"name"</span>   <span class="p">:</span> <span class="s2">"successCountFromPopulation2Sample"</span><span class="p">,</span> | 
 |          <span class="nt">"value"</span>  <span class="p">:</span> <span class="mi">450</span> | 
 |        <span class="p">},</span> | 
 |      <span class="nt">"sample2Size"</span> <span class="p">:</span> | 
 |        <span class="p">{</span> <span class="nt">"type"</span>   <span class="p">:</span> <span class="s2">"constant"</span><span class="p">,</span> | 
 |          <span class="nt">"name"</span>   <span class="p">:</span> <span class="s2">"sampleSizeOfPopulation2"</span><span class="p">,</span> | 
 |          <span class="nt">"value"</span>  <span class="p">:</span> <span class="mi">600</span> | 
 |        <span class="p">}</span> | 
 |      <span class="p">}</span> | 
 |     <span class="p">}</span> | 
 | <span class="p">}</span> | 
 | </code></pre></div> | 
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