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63 lines
1.9 KiB
Markdown
63 lines
1.9 KiB
Markdown
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---
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toc_priority: 301
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toc_title: welchTTest
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---
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# welchTTest {#welchttest}
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对两个总体的样本应用 Welch t检验。
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**语法**
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``` sql
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welchTTest(sample_data, sample_index)
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```
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两个样本的值都在 `sample_data` 列中。如果 `sample_index` 等于 0，则该行的值属于第一个总体的样本。 反之属于第二个总体的样本。
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零假设是群体的均值相等。假设为正态分布。总体可能具有不相等的方差。
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**参数**
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- `sample_data` — 样本数据。[Integer](../../../sql-reference/data-types/int-uint.md), [Float](../../../sql-reference/data-types/float.md) 或 [Decimal](../../../sql-reference/data-types/decimal.md).
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- `sample_index` — 样本索引。[Integer](../../../sql-reference/data-types/int-uint.md).
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**返回值**
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[元组](../../../sql-reference/data-types/tuple.md)，有两个元素:
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- 计算出的t统计量。 [Float64](../../../sql-reference/data-types/float.md)。
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- 计算出的p值。[Float64](../../../sql-reference/data-types/float.md)。
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**示例**
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输入表:
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``` text
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┌─sample_data─┬─sample_index─┐
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│ 20.3 │ 0 │
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│ 22.1 │ 0 │
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│ 21.9 │ 0 │
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│ 18.9 │ 1 │
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│ 20.3 │ 1 │
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│ 19 │ 1 │
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└─────────────┴──────────────┘
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```
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查询:
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``` sql
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SELECT welchTTest(sample_data, sample_index) FROM welch_ttest;
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```
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结果:
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``` text
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┌─welchTTest(sample_data, sample_index)─────┐
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│ (2.7988719532211235,0.051807360348581945) │
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└───────────────────────────────────────────┘
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```
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**参见**
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- [Welch's t-test](https://en.wikipedia.org/wiki/Welch%27s_t-test)
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- [studentTTest function](../../../sql-reference/aggregate-functions/reference/studentttest.md#studentttest)
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