*Section author: Danielle J. Navarro and David R. Foxcroft*

# Descriptive statistics separately for each group¶

It is very commonly the case that you find yourself needing to look at
descriptive statistics broken down by some grouping variable . This is
pretty easy to do in jamovi. For instance, let’s say I want to look at the
descriptive statistics for some clinical trial data, broken down separately by
`therapy`

type. This is a new data set, one that you’ve never seen before.
The data is stored in the `clinicaltrial`

data set and we’ll use it a lot in
chapter Comparing several means (one-way ANOVA)
(you can find a complete description of the data at the start of that chapter).
Let’s load it and see what we’ve got:

Evidently there were three drugs: a placebo, something called “anxifree” and
something called “joyzepam”, and there were 6 people administered each drug.
There were 9 people treated using cognitive behavioural therapy (CBT) and 9
people who received no psychological treatment. And we can see from looking
at the `Descriptives`

of the `mood.gain`

variable that most people did show
a mood gain (mean = 0.88), though without knowing what the scale is here it’s
hard to say much more than that. Still, that’s not too bad. Overall I feel that
I learned something from that.

We can also go ahead and look at some other descriptive statistics, and
this time separately for each type of therapy. In jamovi, check Std.
deviation, Skewness and Kurtosis in the `Statistics`

options. At the
same time, transfer the `therapy`

variable into the `Split by`

box,
and you should get something like Fig. 18.

What if you have multiple grouping variables ? Suppose you want to
look at the average mood gain separately for all possible combinations of
drug and therapy. It is possible to do this by adding another variable,
`drug`

, into the `Split by`

box. Easy peasy, though sometimes if you
split too much there isn’t enough data in each breakdown combination to
make meaningful calculations. In this case jamovi tells you this by
stating something like `NaN`

or `Inf`

.[1]

[1] | Sometimes jamovi will also present numbers in an unusual way. If a
number is very small, or very large, then jamovi switches to an
exponential form for numbers. For example 6.51e-4 is the same as
saying that the decimal point is moved 4 places to the left, so the
actual number is 0.000651. If there is a plus sign (i.e. 6.51e+4
then the decimal point is moved to the right, i.e. 65,100.00. Usually
only very small or very large numbers are expressed in this way, for
example 6.51e-16, which would be quite unwieldy to write out in
the normal way. |