calculate the standard deviation of a group of numbers

You can use the function STDEV(). In the example above:

B2=STDEV(A)

How about if the grouped numbers are in a frequency table such as:

questions correct number of students

5 3

4 2

3 1

2 6

1 4

0 3

Hi Heather,

Standard Deviations are calculated using the individual data for either a whole population or individual data from a representative sample of the whole population. If you do not have the original collection, your first step will be to reconstruct the 'raw' data set. Here's a method using a second table to reproduce the full set from the frequency table you providnces of '2' in the table were derived from original scores of 1,6, 1.7, 1.7, 1.9, 2.0 and 2.4), the STDEV of the calculation may not be correct for the original data.

Here's a sample using a second table to reproduce the full set from the frequency table you provided, and a third table on which to do the standard deviation calculations using three of the four available functions. See below for which will be suitable to your data.

Frequency is your frequency table. I've re-sorted it with values ascending in column A, but this is not necessary.

Original is a table used to reconstruct the original set of values from the frequency table.

Row 1, a header row, contains integers indicating the count of each value in the frequency table. You will need at least as many columns as the highest count in the frequency table.

In the body of the table, starting at Row 2, you will need one row for each value in the first column of the frequency table.

There is one formula on this table, entered in cell A2, then filled right and down to all other cells in the table.

=IF(Frequency :: $B2<A$1,"",Frequency :: $A2)

Note that the cells in this table that appear 'empty' actually contain a null string ( "" ), which is a text value.

STDEV is a table in which the standard deviation for the data set is calculated, using the set in the table "Original".

It contains one formula, entered in cell B2:

=STDEV(Original :: $A$2:$I$7)

Numbers provides four functions to calculate the standard deviation: STDEV, STDEVA, STDEVP and STDEVPA

STDEV is used if the data is from a sample of the whole population.

STDEVP is used if the data is from all individuals in the whole population.

Both of these functions ignore text values and boolean values.

The same functions with the A added are used when the data includes boolean (TRUE/FALSE) and/or text data. TRUE is assigned a numerical value of 1, FALSE is assigned a numerical value of zero, and all text values are assigned a value of zero.

Regards,

Barry