if you've ever wondered what a fold change is referring to when it's used in medical research
context in the context of data analysis then this video is for you. A fold change has nothing to
do with folding.. yeah i know surprising fold change is simply a ratio it measures the number
of times that something has changed for example if you are comparing an experimental group in a
control group you will divide the results for the experimental group by that of the control group
if you're measuring a signal over time you may want to look at the signal in reference to the
very first time point or you may want to look at the signal from the latest time point to the
one just before it the previous time point as an example let's say the intensity that i got
for protein expression for one time point was this value then i can look
at and this was the experimental group then i can look at the control group and the control
group has this value so to look at i may want to see what's the fold change what's the ratio here
so i can just go ahead and do the experimental group and divide that by the control group
sometimes it may be more meaningful to look at the percentage difference so actually the
difference is what you are concentrating on so in this case you will take away the
value the new value you take away the initial value and then divided by the initial value
and often it's also meaningful to present it
as a percentage so you multiply it per 100 and that just makes it easier to get meaning
now if for example we're looking at an antibody response following
infection we may easily report it as a fold change so we will get the original
expression the original quantity which we may have measured via Western blot or an ELISA:
enzyme-linked immunosorbent essay so then we can just simply divide into the original amount that
we got it's just a ratio of the results then easily express that to make it meaningful at
a glance as a percentage and that's just by multiplying it by a hundred how about d3 we
would simply just divide that value into the original so we'll divide the signal at
the new time point or the day by the signal at the beginning like the initial infection
so what we see that we have a nine fold change it's 9.8 so almost a ten-fold change
from the first the day one post infection to this uh second we have almost a ten-fold change then
by day three between day three and the and the day one there's a uh 1.74 fold change and
so on and so forth for the remainder of the data and then you can just look at that in terms
present that as percentage just to make it easier for your audience for the person looking at your
data to just immediately get a sense of what that means so if we just multiply that by a hundred
we may also want to present the data in terms of the difference in the data rather than the
absolute fold change and in that case it's our new value minus the original divide by
the original present that as percentage just to make it easier for your audience
when i leave the number just as the difference without multiplying by a hundred you can see
you know point two two point two two is a small value it's not immediately clear to someone what
you know they don't get a good sense of the number because we don't normally deal with
that kind of scale so just by multiplying by 100 we'll get a sense we'll... it will be like 22
and yeah we're comfortable with that so it's good to scale it to a percentage
if we want the rest of the cells to be calculated without us going through this process
of doing it ourselves we simply constrain the cell by just placing a dollar sign in
front of it so we place the dollar sign in front of the row as well as the column
and then by dragging it down excel noise to do exactly the same thing for the res the
remainder of the cells and then we can go ahead and plot it and plot in excel is super easy
you just have to select the two columns that you want to plot and go to insert and you
can select the type of chart that you want so for this kind of time series or related
data it is best to use a line graph or a scatter graph we can use a line graph in this case because
it is related and we can go ahead and and it will automatically have a line that tracks it for us
and just by making some simple adjustments we can make the graph look really attractive now i
will not go into too much detail because this is just on fold change and on the percentage
difference calculations if you would like to see the graphs done in excel then please let me know
but i will leave it here for now and if you are interested in joining the study group go ahead
and hit the subscribe button and i will catch you in the next video God bless you and take care.