118 lines
4.0 KiB
Markdown
118 lines
4.0 KiB
Markdown
---
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id: test-stats
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title: "Test Stats Aggregators"
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---
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<!--
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This Apache Druid extension incorporates test statistics related aggregators, including z-score and p-value. Please refer to [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/) for math background and details.
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Make sure to include `druid-stats` extension in order to use these aggregators.
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## Z-Score for two sample ztests post aggregator
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Please refer to [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/) and [http://www.ucs.louisiana.edu/~jcb0773/Berry_statbook/Berry_statbook_chpt6.pdf](http://www.ucs.louisiana.edu/~jcb0773/Berry_statbook/Berry_statbook_chpt6.pdf) for more details.
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z = (p1 - p2) / S.E. (assuming null hypothesis is true)
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Please see below for p1 and p2.
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Please note S.E. stands for standard error where
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S.E. = sqrt{ p1 * ( 1 - p1 )/n1 + p2 * (1 - p2)/n2) }
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(p1 – p2) is the observed difference between two sample proportions.
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### zscore2sample post aggregator
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* **`zscore2sample`**: calculate the z-score using two-sample z-test while converting binary variables (***e.g.*** success or not) to continuous variables (***e.g.*** conversion rate).
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```json
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{
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"type": "zscore2sample",
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"name": "<output_name>",
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"successCount1": <post_aggregator> success count of sample 1,
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"sample1Size": <post_aggregaror> sample 1 size,
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"successCount2": <post_aggregator> success count of sample 2,
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"sample2Size" : <post_aggregator> sample 2 size
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}
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```
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Please note the post aggregator will be converting binary variables to continuous variables for two population proportions. Specifically
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p1 = (successCount1) / (sample size 1)
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p2 = (successCount2) / (sample size 2)
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### pvalue2tailedZtest post aggregator
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* **`pvalue2tailedZtest`**: calculate p-value of two-sided z-test from zscore
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- ***pvalue2tailedZtest(zscore)*** - the input is a z-score which can be calculated using the zscore2sample post aggregator
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```json
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{
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"type": "pvalue2tailedZtest",
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"name": "<output_name>",
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"zScore": <zscore post_aggregator>
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}
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```
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## Example Usage
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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.
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A JSON query example can be as follows:
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```json
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{
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...
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"postAggregations" : {
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"type" : "pvalue2tailedZtest",
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"name" : "pvalue",
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"zScore" :
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{
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"type" : "zscore2sample",
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"name" : "zscore",
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"successCount1" :
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{ "type" : "constant",
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"name" : "successCountFromPopulation1Sample",
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"value" : 300
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},
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"sample1Size" :
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{ "type" : "constant",
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"name" : "sampleSizeOfPopulation1",
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"value" : 500
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},
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"successCount2":
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{ "type" : "constant",
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"name" : "successCountFromPopulation2Sample",
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"value" : 450
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},
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"sample2Size" :
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{ "type" : "constant",
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"name" : "sampleSizeOfPopulation2",
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"value" : 600
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}
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}
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}
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}
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```
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