Direction of difference: confidence interval for independent samples t-test

[Returner]

I am using the function t.test to perform the independent samples t-test in R Studio. I have included the argument 'conf = 0.95' to obtain a 95% CI for the difference in population means. I am surprised to note that the output does not automatically include the difference in means corresponding to the reported CI limits. Could I please have advice on:

a) how R decides which way round, by default, to calculate the difference in sample means and corresponding differences for the CI limits;

b) whether I can include an extra argument in t.test to request that the difference in sample means is included in the output;

and

c) whether I can control which way round the difference is calculated for the CI limits when using the argument "conf=0.95".

It may help to note that the categories for my group variable are included as text names rather than numbers in my dataset.

Also, I can see that in any one case, it is possible to use the t-statistic value generated to deduce which way round the difference in means was calculated. However, I would prefer to have a more general insight in the senses reflected in my above queries.

Many thanks in advance!

[HanOostdijk]

Type

stats:::t.test.default

to see the code of the function. This may help.

[Returner]

Thank you for this thoughtful suggestion. I have had a look at the code that is returned on running this request. However, unfortunately, it does not provide an answer to my query. I am running the independent samples t-test from a datafile which already contains the relevant dependent and independent variables and wish to know how R decides which way round to subtract the means represented by the categories of the independent variable, which are currently expressed as text names.