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A11. Time Series
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welcome back we will now discuss time
series as part of your data analysis
under analyze face time series is a
sequence of observations over regularly
spaced intervals of time as mentioned
the time series chart is used to track
the performance of your data or your
process over time example of
applications are monthly unemployment
rates for the previous five years daily
production at a manufacturing plant for
a month they get by decade population of
a state of the previous century it can
also include your SL age or service
level agreements which are monitored on
a monthly basis or the number of
customers that you have served for the
past weeks on a daily basis or on a
monthly basis or the number of incidents
of mishaps in an organization which is
recorded on a monthly basis as long as
you are trying to monitor or check the
performance of your data regardless of
its type either continuous or attribute
or discrete you can use time series as
long as your x-axis is a unit of time
now let's do on the anatomy of a time
series chart as you can see here we have
the y axis which corresponds to a
continuous variable which is gold price
on a dollar per ounce and your x axis
which is here as you can see here there
are data points that are plotted across
time and here are the time elements
remember that you can only use line
chart when you're using time series not
using bar child so that's the common
mistake that visual analysts do commit
using bar charts when their x axis is a
unit of time so always use the time
series chart on those particular
applications why do we use time series chart
chart
generally speaking we use time series
chart because we want to look for
patterns or we want to observe how our
process output behave across time we are
looking for what we call patterns which
can be further subdivided into 3 which
are trend
shift or cycle let's go with trend a
trend is a series of data points that is
increasing or decreasing increasing
the time decreasing attendance rate
increasing rejection rate so those are
possible scenarios that we can see next
is chef chef means an old performance
shifting to a new level of performance
either because of an improvement or
either because of a problem now as you
can see here there is a group of data
points here which shifted downward so
this is a particular example let's say
this is the current performance of your
attendance rate for the past weeks and
then it suddenly drop or this could be
the performance of your yield and it
suddenly drop due to something that
happened when you detect shift there has
been a sudden change of an element of
the process that triggered this
particular shift next cycle cycle as
represented by waves like this this
could also mean a CSUN
so when you say cycle it's a repetitive
cyclical movement of your data points
from one series of time periods to
another let's say holiday there could be
holiday season or cycle so those are
example of cycle though we can have as
we look on our time series chart now in
using time series chart this is the
important patterns that we have to look
for if in case we found out any of this
we should ask ourselves what happened to
our process why is it giving us this
kind of patterns let's take our first
example as we use time series flood the
manager of a shipping yard wants to
study the amount of cargo that is
transported the manager collects the
weight of all cargo that passes through
the shipping yard each month now we will
go to our source sheet and copy our data
shipping to our Minitab so let's look
for our shipping data and our source
worksheet just have to copy this and
then go to our Minitab again you have to
paste your data on the first row here
without the CRO numbers now we have two
columns the month running through more
than 50 and 100 seven months of data and
this is the weight of the material ship
when using time series we can go either stat
stat
we have an option here time-series or we
can go to graph we have an option here
so for this case we'll go to graph again
time series plot plot the data in the
order that it appears in the worksheet
okay so whatever you are giving the
Minotaur software it will just plot it
based on the order so let's go to graph
and then click time series let's use
simple because we have one set of data
here one column and then you just have
to click your weight data here which
data columns do you want operate a time
series plot so double left-click that
particular column for this case C 2
double left-click and then you just have
to click OK
okay so we have now a time series of
weight across 107 months so this is your
y axis corresponding to your rate data
across 107 months and these are the data
plotted all over those periods do you
see any patterns okay so for this case
we have this lump of data points here
I think this would mean a shift from
here to here okay and there's a natural
cycle as you can see several number of
trends decreasing trend we have
increasing trend increasing trend
decreasing trend those patterns are
available now what we want to do is to
understand the behavior of our process
why it exhibits this patterns and make
it as a basis for us to further
investigate now when you're using time
series for your hypothesis testing or
root-cause validation you just have to
state your hypothesis and if your data
and if you want to prove that using your
data and check it across time then you
can use time series let's say is there
any dependency of your problem - let's
say the day of the week or week of the
month now you can use time series to
prove that so that's the first example
let's go to the next example the
administrator of a hospital wants to
examine the number of courage' patients
admitted over the past 24 months to
analyze trends in the
so for this case we will be using the
patient data so let's go to our
worksheet patient and then let's copy
the data let's go back Minitab create
new worksheet by pressing ctrl n and
close this graph now we can paste a data
so we have two columns again this time
it's indicated here on the first call of
the month but this data we only get the
first 12 months of a year we didn't
include the second set of twelve months
and this column corresponds the number
of cards of patients now what we want to
do is to create a time series chart
graph time series simple let's erase
this and replace with number of patients
now before you click OK you can actually
specify the time for scale because you
have C one month for you to replace the
index one to twelve we can click
timescale and then click stamp click on
this dialog box here and then the
available stamp column will appear so
you want to stomp the x-axis with the
month corresponding to the data points
and then you can click OK and then click
ok now we have your time series chart of
the number of patient cards of patients
over one year now do you see patterns
yes there is an increasing pattern here
from October November and December and
there is a decreasing pattern here from
January February March and April there
could be a possible shift this lump of
data going to this lump of data and
another shift here there could be cycle
if we replicate this one we move to the
next year we can see cycle now the
question is why is there this particular
behavior of this process or output data
this is number of cards of patients over
a year you can see that in November and
December there has been an increase
until January February and March
it's because do you have any guess yes
it's because of the festivities or the
holiday so this is a data from the US we
have November December those months
until March those are festivities we
just the reason why the number of cards
of patients should up on this month by
understanding how the process output
behave over time can give us insights
and how we can do our actions or
improvement actions moving forward
validating also our claims if let's say
is months a significant factor on the
number of courage of patients if that's
your hypothesis or is the number of
project patients dependent on the month
if that's the case then the answer will
be yes as seen in this particular output
chart that we have moving forward this
is how you will validate your hypothesis
if you have a continuous data or an
attribute data as your Y and a unit of
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