ClickHouse/docs/zh/sql-reference/aggregate-functions/reference/welchttest.md
2022-04-10 17:08:18 -06:00

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---
sidebar_position: 301
sidebar_label: welchTTest
---
# welchTTest {#welchttest}
对两个总体的样本应用 Welch t检验。
**语法**
``` sql
welchTTest(sample_data, sample_index)
```
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。
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。
**参数**
- `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).
- `sample_index` — 样本索引。[Integer](../../../sql-reference/data-types/int-uint.md).
**返回值**
[元组](../../../sql-reference/data-types/tuple.md),有两个元素:
- 计算出的t统计量。 [Float64](../../../sql-reference/data-types/float.md)。
- 计算出的p值。[Float64](../../../sql-reference/data-types/float.md)。
**示例**
输入表:
``` text
┌─sample_data─┬─sample_index─┐
│ 20.3 │ 0 │
│ 22.1 │ 0 │
│ 21.9 │ 0 │
│ 18.9 │ 1 │
│ 20.3 │ 1 │
│ 19 │ 1 │
└─────────────┴──────────────┘
```
查询:
``` sql
SELECT welchTTest(sample_data, sample_index) FROM welch_ttest;
```
结果:
``` text
┌─welchTTest(sample_data, sample_index)─────┐
│ (2.7988719532211235,0.051807360348581945) │
└───────────────────────────────────────────┘
```
**参见**
- [Welch's t-test](https://en.wikipedia.org/wiki/Welch%27s_t-test)
- [studentTTest function](../../../sql-reference/aggregate-functions/reference/studentttest.md#studentttest)