help digituse
-------------------------------------------------------------------------------

Title

    digituse -- Tabulate the pattern of digit use in a variable

Syntax


        digituse varname [, places(#)]


Description

    The digituse function displays the proportionate use of the digits 0-9 in
    each significant digit of a variable. The number of places to the right
    of the decimal point can be defined using an option.  The number of
    places to the left of the decimal point is automatically set as required
    by the maximum value stored in the variable.


Options

        +---------+
    ----+ General +----------------------------------------------------------

    places(#) indicates the number of decimal places which should be
        examined.  The default is 9 which often shows rounding errors in the
        extreme places.  Generally you should specify at least one more
        decimal place than the expected number of places: and then expect the
        extra place to contain 100% zeros and no other digits.

Remarks

    This function outputs a table in which a series of columns of percentage
    values indicate the proportionate use of digits in each significant digit
    of the variable.  These percentages are rounded to integers so an entry
    of zero indicates some instances of that digit were found in the
    indicated place.  An entry of '.' indicates no instances of the digit
    were found at that place.

    The following annotated example of the output shows how this function can
    be used:

    . digituse sodium, places(3)
    ------------------------------------
     Digit | Position (10^)
           |    2   1   0  -1  -2  -3
    -------+----------------------------
       0   |    1   1  16 100 100 100
       1   |   99   0  15   .   .   .
       2   |    .   1  12   .   .   .
       3   |    .  44   8   .   .   .
       4   |    0  54   6   .   .   .
       5   |    .   0   5   .   .   .
       6   |    .   0   5   .   .   .
       7   |    .   .   8   .   .   .
       8   |    .   0  10   0   .   .
       9   |    .   .  15   .   .   .
    ------------------------------------

    In the 10^2 column (hundreds), the zero suggests there are a small number
    of values in the 400's range while the 1 and 99 clearly indicate most
    values are in the 100's with a small proportion below this.

    The 44 and 54 in the second columns extend this knowledge and show that
    most values are in the 130s and 140s, suggesting the one or more 400s are
    outliers and should be investigated.

    The grouping of values in the third column suggests most values end with
    an 8, 9, 0, 1 or a 2 (i.e. fall between 138 and 142).

    The 100 values in the fourth, fifth and sixth columns indicate the
    majority of values have zero in the tenths, hundredths and thousands.
    However the zero in the tenths column shows that at least one value has
    an 8 in this position.  This is clearly an anomaly and worthy of further
    investigation.  The zerouse function could be used to identify these
    cases.


Examples

    . digituse y1
    . digituse y1, places(3)

Author

    Richard J. Atkins
    London School of Hygiene and Tropical Medicine
    e-mail: richard.atkins@lshtm.ac.uk