Grouping Data: Frequency Distribution Table Video Lecture - Class 8

welcome back this is a statistics video
that is talking about frequency
distribution tables this time we're
looking at how we process grouped data
okay the question asks us to arrange the
following data to enter a frequency
distribution table there are a bunch of
numbers here and they want us to if
we're going to process them in a group
to way here it's logical to for us to
put in put in classes here that indicate
just the ten so these might be test
scores
we might just overall instead of
focusing on individual scores here we
might want to know globally how many
people scored in the 50s how many people
scored in the 60s etc right up to the
90s just for a quick overview of how
students went in the test so that might
be a reason for doing that okay so you
notice the heading there there these are
classes or groups that we're putting
these things in and what we do when we
get have group scores is we have what we
call a class center which represents
it's a single score or a particular
value here that represents the group now
a logical way to place it a logical
place to look for a score that to
represent a group is to get something
that's right in the middle of it and so
we want really the middle or the class
center the center of these two extremes
that describe the group now the way to
get that is to add those to score the
two edges of the groups together 50 plus
59 if we did 50 plus 50 9 divided by 2
we would find the the center of that
particular class so if we add that up we
find the mid the middle point it's
actually kind of like the center of that
group each time 54.5 we're going to
quote as the class center now that's not
all that necessary at the moment but it
will become necessary later on when we
calculate other statistical items from
this frequency distribution table so
don't be surprised when you're looking
at group data frequency distribution
tables that you have a column called
class Center we won't use it all that
much in this one but for each of those
groups it's going to work the same way
and we're going to have class centers of
sixty four point five seventy four point
five etc now
we get that we add these two numbers
together and divide by two we basically
take the average of those two numbers
and we get a class center to use later
on or to graph with that sort of thing
so that often happens but for our
purposes today we're just going to put
each of these individual scores into
their class and add up how many of these
scores occur apply or are owned by these
different classes so let's have a look
we'll cross off 65 and we'll put a tally
mark in the class that 65 should belong
to 65 is between 60 and 69 so we'll put
a telling mark on that one we'll just
ignore the class centers for now we're
really focusing on these classes here
and whether the individual scores
belonged to each of those classes so
we'll cross off 73 and put a marking
down in the 70s 64 is another tally mark
for the 60s 85 is in the 80s obviously
we just keep crossing each individual
score off and putting a tally mark down
in the class that it belongs to 77 82 93
86 63 goes in the 60s 58 goes in the 50s
now this next marking we've already got
for tally marks in the 60s and we're
just about to add another one to it and
just want you to be aware of how we do
that we cross off the 63 and we'll put a
diagonal mark there we do that so it
makes it easier to add up the telling
marks later on rather than having just a
whole bunch of vertical telling marks
every every fifth one we do a diagonal
62 gives us another tally in the 60s 79
another one in the 70s sixty one goes
there
74 goes there okay so we've tallied up
how many scores occur or belong to each
of those classes appropriately now we'll
just fill in the frequency table from
that so that one tally mark for the 50s
so there's a 50s occur once there are
seven scores in the 60 to 69 category so
that's got a freak
see that class has this frequency of
seven there are four markings they're
pretty obvious the way to fill in that
frequency bit so we think we're done
well just do a double check to make sure
we haven't missed any scores I mean
crossing off the scores as we did at the
top helps us a lot so we don't miss any
just do things carefully one at a time
but there's a double check we can use
we'll add up the number of scores that
we have and apparently there's 16 of
them I'm here to tell you and we can
double check that we haven't missed any
by adding up our frequency column and
making sure we've processed sixteen
scores onto our table here so 7 plus 1
plus 7 is 8 plus 4 is 12 plus 3 is 15
plus 1 is 16 so that account of the
original scores tallies up nicely and
agrees with the total of the frequency
column we should be confident that we've
done everything pretty correctly there
so that's how we tally up the and
construct a frequency distribution table
and this time with grouped data we did
find the class center each time but
we'll worry about that in future videos
so there we have it frequency
distribution tables using grouped data
alright see you next time Peter Blake
NASSCOM