We need to start with some data. We will generate a list of data on the calculator using GNRND4 with Key 1=192338704 and Key 2=9000524. That list will be the same numbers that appear in the following table: Thus, our problem will be to generate a frequency table for the data in the list above.
Before we even start the problem we need to spend a moment explaining why we are treating this as continuous data. Clearly these are integer values. Individually they do not look any different from the values that we used when we did our analysis of discrete data before. However, in the 88 values given above we have 80 different values. That means that at least 72 values appear just once. It would not tell us very much if we were to use COLLATE2 to find all of those different values and to look at teh frequency of each. Almost all will have a frequency of 1. Therefore, we need a different approach. We treat the values as continuous. We will divide the range of values into even intervals. Then we will count the number of items in each interval.
![]() | Figure 1 starts with a run of the GNRND4 program where we have entered the two key values given above. | |
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In Figure 2 we can see the start of the list of values. We recall that the list is
created by GNRND4 as L1. Also note that
we had pressed the ![]() | |
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For the sake of being able to return to the original lsit, we will make a copy of the
list. The keys to do this are
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To sort the values in L2
we need to get the proper command.
Press ![]() ![]() ![]() ![]() | |
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We finish the command by pressing
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Now we know that the lowest value is 333. We could find the highest value if we asked the calculator to display the last position in L2. We could count the values in the table above, or we could just ask the calculator to tell us the size of L2. The latter alternative is more appealing. the command we want is dim(L2). | |
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We return to the LIST menu, the OPS sub-menu, and select the dim( option. | |
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We complete the command with ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() | |
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We want to examine the values in L2.
We can use the STAT Editor to do that, but, given our earlier use
of some lists produced by COLLATE2, it would be good to reset
the editor to display the built-in lists. We return to the
STAT menu and SetUpEditor option by
pressing the ![]() | |
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Once the SetUpEditor command has been pasted on the screen, we press
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Once in the editor, we move to the second column by using the
![]() This screen shows the sorted values in L2. We know that we want the first "class" of values to run from 330 to just before 380. Looking at these values we see that we have 6 items (333, 341, 343, 345, 373, and 379) in this class. Then we can move down the list to see more values. | |
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Our next class has limits 380 to just before 430.
There are 4 items in this class (400,403, 407, 425).
We should note that we could have used the index values, shown for the highlighted item as the bottom of the screen, to produce the number of items between two items. Thus, if we know the index of the first item in the class and the index of the last item in the class we can compute the number of items in the class as class size = 4 | |
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Here are more items. This is a long list and we have many more such screens to examine in this brute stength and awkwardness approach of counting items. | |
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Class limits | Frequency |
330 ≤ x < 380 | 6 |
380 ≤ x < 430 | 4 |
430 ≤ x < 480 | 14 |
480 ≤ x < 530 | 22 |
530 ≤ x < 580 | 17 |
580 ≤ x < 630 | 16 |
630 ≤ x < 680 | 7 |
680 ≤ x < 730 | 2 |
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An alternative approach to getting the values for the frequency table
is to let the calculator create a histogram of the data and then we can
manipulate the WINDOW settings to correspond to the
class limits that we want to use. To do this we start by
reviewing the plot settings. Press
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Figure 15 shows the current settings for Plot1. Use the cursoe keys to move the highlight to the value after Xlist: as shown in Figure 16. |
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Now we can change this setting. To change it
to L1 press
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The settings are as we want. We can move directly to
the ZOOM menu by pressing the ![]() |
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The option we want is ZoomStat and we need to move down to that option. Selecting this option, when we have a Plot set to do as Historgram as we do, will cause the calculator to examine the values in the list associated with that Plot and to set some seemingly appropriate WINDOW values for that data. Then calculator displays the resulting Histogram. |
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Figure 19 shows the histogram with the class width and lower class limit that the
calculator set. To see these values we move to the
WINDOW screen by pressing ![]() |
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These are the values that the calculator determined. We can change these and then display a new histogram. |
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We set Xmin to be the desired lower limit for the first class, in our case that would be 330.
We set Xscl to 50 to make the class width 50.
Because we want to include all of the data we set the
Xmax value to be what would be the lower limit of the next class above our
highest data value. [Note that frow our earlier work we know that highest value
is 728, a value that we cannot determine from the original WINDOW settings.]
Press |
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The histogram shown in Figure 22 corresponds to the
frequencies that we found earlier by examining all of the sorted data.
If we had not done that examination we could still have produced this
histogram. In that case, we would want to use the histogram to get the values.
We can do this by moving into "trace" mode by
pressing ![]() |
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In "trace" mode the calculator highlights the first column
and displays the information that the column
represents values from 330 up to but
not including 380 and that there were 6 values in this class.
We press ![]() |
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From this display we see that the second class has 4 items in it. |
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Moving to the third class we see that it has 14 items. We could continue to move across the chart to determine the frequency in each class. From this we could build the table that we constructed before Figure 14. |
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We press ![]() ![]() |
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That action pastes the command prgmCOLLATE3 onto the main screen.
We press ![]() |
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The program starts and asks us for the
location of the input data. Ours is in
L1 so we press
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The program tells us the lowest value in the list, 333, and the highest value in the list, 728. The program suggests a lower limit value for the first class, but we do not need to use that suggestion. In fact, we know that we want to use 330 as the first lower limit. We enter that value. |
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The program then suggests a class width to use, but we can make our own choice, which in this case we set to be 50. |
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The progam reports that it found 88 values and has put them into 8
classes. It then gives us some additional information.
The calculator is in a "pause" condition so that we can read the information.
We press ![]() |
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The progam concludes after showing us more information. Behind the scenes COLLATE3 has created some additional lists and it has reset the Stat Editor to display these lists. We move to the Stat Editor to see these values. |
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The first column, Low, gives the lowerr limit of each class. The second column, ICNT, gives the frequency of items in each class. These are the same values we found earlier. The third column, RFREQ, gives the relative frequency for each class. |
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Here we have moved down the lists to see the final class values. We do note that the first class has one extra entry. That is there to show the lower limit of the next class if it were there. We use that as the upper limit of the previous class. |
©Roger M. Palay
Saline, MI 48176
September, 2012