VAR_SAMP

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SELECT
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  survey_wave,
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  AVG(satisfaction_score) as avg_satisfaction,
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  VAR_SAMP(satisfaction_score) as variance,
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  STDDEV_SAMP(satisfaction_score) as stddev,
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  COUNT(*) as sample_size
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FROM `project.dataset.customer_survey`
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GROUP BY survey_wave
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ORDER BY survey_wave;

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SELECT
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  'Group A' as group_name,
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  VAR_SAMP(value) as variance,
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  COUNT(*) as n
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FROM `project.dataset.experiment_a`
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UNION ALL
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SELECT
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  'Group B' as group_name,
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  VAR_SAMP(value) as variance,
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  COUNT(*) as n
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FROM `project.dataset.experiment_b`;

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SELECT
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  SUM((n - 1) * var_samp) / SUM(n - 1) as pooled_variance
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FROM (
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  SELECT
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    treatment_group,
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    VAR_SAMP(outcome) as var_samp,
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    COUNT(*) as n
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  FROM `project.dataset.clinical_trial`
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  GROUP BY treatment_group
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);

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SELECT
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  product_id,
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  AVG(daily_sales) as mean_sales,
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  SQRT(VAR_SAMP(daily_sales)) as sales_stddev,
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  SQRT(VAR_SAMP(daily_sales)) / AVG(daily_sales) * 100 as cv_percent
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FROM `project.dataset.daily_product_sales`
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GROUP BY product_id
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HAVING COUNT(*) >= 30
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ORDER BY cv_percent DESC
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LIMIT 10;