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74 lines
2.7 KiB
Markdown
74 lines
2.7 KiB
Markdown
---
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slug: /en/sql-reference/aggregate-functions/reference/mannwhitneyutest
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sidebar_position: 310
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sidebar_label: mannWhitneyUTest
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---
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# mannWhitneyUTest
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Applies the Mann-Whitney rank test to samples from two populations.
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**Syntax**
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``` sql
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mannWhitneyUTest[(alternative[, continuity_correction])](sample_data, sample_index)
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```
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Values of both samples are in the `sample_data` column. If `sample_index` equals to 0 then the value in that row belongs to the sample from the first population. Otherwise it belongs to the sample from the second population.
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The null hypothesis is that two populations are stochastically equal. Also one-sided hypothesises can be tested. This test does not assume that data have normal distribution.
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**Arguments**
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- `sample_data` — sample data. [Integer](../../../sql-reference/data-types/int-uint.md), [Float](../../../sql-reference/data-types/float.md) or [Decimal](../../../sql-reference/data-types/decimal.md).
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- `sample_index` — sample index. [Integer](../../../sql-reference/data-types/int-uint.md).
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**Parameters**
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- `alternative` — alternative hypothesis. (Optional, default: `'two-sided'`.) [String](../../../sql-reference/data-types/string.md).
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- `'two-sided'`;
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- `'greater'`;
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- `'less'`.
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- `continuity_correction` — if not 0 then continuity correction in the normal approximation for the p-value is applied. (Optional, default: 1.) [UInt64](../../../sql-reference/data-types/int-uint.md).
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**Returned values**
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[Tuple](../../../sql-reference/data-types/tuple.md) with two elements:
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- calculated U-statistic. [Float64](../../../sql-reference/data-types/float.md).
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- calculated p-value. [Float64](../../../sql-reference/data-types/float.md).
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**Example**
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Input table:
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``` text
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┌─sample_data─┬─sample_index─┐
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│ 10 │ 0 │
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│ 11 │ 0 │
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│ 12 │ 0 │
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│ 1 │ 1 │
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│ 2 │ 1 │
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│ 3 │ 1 │
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└─────────────┴──────────────┘
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```
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Query:
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``` sql
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SELECT mannWhitneyUTest('greater')(sample_data, sample_index) FROM mww_ttest;
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```
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Result:
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``` text
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┌─mannWhitneyUTest('greater')(sample_data, sample_index)─┐
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│ (9,0.04042779918503192) │
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└────────────────────────────────────────────────────────┘
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```
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**See Also**
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- [Mann–Whitney U test](https://en.wikipedia.org/wiki/Mann%E2%80%93Whitney_U_test)
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- [Stochastic ordering](https://en.wikipedia.org/wiki/Stochastic_ordering)
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