# Big Data Solutions: A/B t test

@drsimonj here to share my code for using Welch’s *t*-test to compare group means using summary statistics.

## Motivation

I’ve just started working with A/B tests that use big data. Where once I’d whimsically run `t.test()`

, now my data won’t fit into memory!

I’m sharing my solution here in the hope that it might help others.

## In-memory data

As a baseline, let’s start with an in-memory case by comparing whether automatic and manual cars have different Miles Per Gallon ratings on average (using the `mtcars`

data set).

```
t.test(mpg ~ am, data = mtcars)
#>
#> Welch Two Sample t-test
#>
#> data: mpg by am
#> t = -3.7671, df = 18.332, p-value = 0.001374
#> alternative hypothesis: true difference in means is not equal to 0
#> 95 percent confidence interval:
#> -11.280194 -3.209684
#> sample estimates:
#> mean in group 0 mean in group 1
#> 17.14737 24.39231
```

Well… that was easy!