---
title: corr() | Tiger Data Docs
description: Calculate the correlation coefficient from a counter aggregate
---

Since [1.3.0](https://github.com/timescale/timescaledb-toolkit/releases/tag/1.3.0)

Calculate the correlation coefficient from a counter aggregate. The calculation uses a linear least-squares fit, and returns a value between 0.0 and 1.0, from no correlation to the strongest possible correlation.

## Samples

Calculate the correlation coefficient to determine the goodness of a linear fit between counter value and time.

```
SELECT
    id,
    bucket,
    corr(summary)
FROM (
    SELECT
        id,
        time_bucket('15 min'::interval, ts) AS bucket,
        counter_agg(ts, val) AS summary
    FROM foo
    GROUP BY id, time_bucket('15 min'::interval, ts)
) t
```

## Arguments

The syntax is:

```
corr(
    summary CounterSummary
) RETURNS DOUBLE PRECISION
```

| Name      | Type             | Default | Required | Description                                                                                                                     |
| --------- | ---------------- | ------- | -------- | ------------------------------------------------------------------------------------------------------------------------------- |
| `summary` | `CounterSummary` | -       | ✔        | A counter aggregate created using [`counter_agg`](/docs/reference/toolkit/counters-and-gauges/counter_agg/counter_agg/index.md) |

## Returns

| Column | Type             | Description                                                                                                               |
| ------ | ---------------- | ------------------------------------------------------------------------------------------------------------------------- |
| corr   | DOUBLE PRECISION | The correlation coefficient calculated with time as the independent variable and counter value as the dependent variable. |