I have two groups and a variable of interest

I know how to do a two sided t-test to test if the means are different.

t.test(data$pv1~data$IND)

How do I have to code a one sided t-test if I have the hypothesis that the mean of one group is bigger?

I have two groups and a variable of interest

I know how to do a two sided t-test to test if the means are different.

t.test(data$pv1~data$IND)

How do I have to code a one sided t-test if I have the hypothesis that the mean of one group is bigger?

The t.test function has an argument named *alternative* which can be set to two.sided, less, or greater. You can read about the complete options by running

```
?t.test
```

Here is an example with some invented data.

```
x = rnorm(n = 100, mean = 1, sd = 0.1)
y = rnorm(n = 100, mean = 1.3, sd = 0.1)
t.test(x= x, y = y, alternative = "greater")
#>
#> Welch Two Sample t-test
#>
#> data: x and y
#> t = -22.147, df = 195.32, p-value = 1
#> alternative hypothesis: true difference in means is greater than 0
#> 95 percent confidence interval:
#> -0.3142285 Inf
#> sample estimates:
#> mean of x mean of y
#> 1.017068 1.309476
t.test(x= x, y = y, alternative = "less")
#>
#> Welch Two Sample t-test
#>
#> data: x and y
#> t = -22.147, df = 195.32, p-value < 2.2e-16
#> alternative hypothesis: true difference in means is less than 0
#> 95 percent confidence interval:
#> -Inf -0.2705878
#> sample estimates:
#> mean of x mean of y
#> 1.017068 1.309476
```

^{Created on 2020-08-20 by the reprex package (v0.3.0)}

This topic was automatically closed 21 days after the last reply. New replies are no longer allowed.

If you have a query related to it or one of the replies, start a new topic and refer back with a link.