help digit
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Title

    digit -- Extracts digits at a specified decimal place

Syntax

        egen [type] newvar = digit(varname) [, digit(#) round(#) ]

Description

    The digit function extends the egen command.  When used as described
    above, a new user-named variable newvar is created. For each case, newvar
    contains the digit (0 to 9) that is located at a specified decimal
    position in varname.

    Options are available to specify the decimal position that you wish to
    examine as well as any rounding that should be applied to the variable
    when extracting this digit.


Options

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

    Digit(#) indicates the digit you wish to extract.  This is specified
        using the decimal exponent or power of 10 of the desired digit (e.g.
        digit(0) extracts the 'units' digit, digit(1) extracts the 'tens'
        digit, and digit (-2) extracts the 'hundredths' digit).  The detault
        setting is zero (extraction of the 'units' digit).

    Round(#) indicates the number of decimal places to which varname will be
        rounded prior to extracting digit information.  When using the
        command repetitively to extract a series of digits, this option
        should be constant to prevent inconsistencies due to different
        rounding schemes being applied.  The default setting is 15 decimal
        places, however in some cases this may result in rounding errors
        where the number being stored exceeds the available precision. This
        is often the case where floating point values have been imported from
        other data formats using third-party data conversion programs (e.g. a
        number may have been stored as 4.9999999999997 instead of 5).

Remarks

    This function creates a new variable containing the digit stored at a
    certain decimal position in an existing variable.  This new variable can
    be tabulated to investigate digit preferences.

    The following example illustrates how this function can be used:

    . egen hundredths = digit(potass), digit(-2) round(2)
    
    . tab hundredths
    ------------------------------------------------
    10^-2 digit |
     of potass  |      Freq.     Percent        Cum.
    ------------+-----------------------------------
              0 |     13,468       93.72       93.72
              1 |         84        0.58       94.31
              2 |        114        0.79       95.10
              3 |        105        0.73       95.83
              4 |         96        0.67       96.50
              5 |        109        0.76       97.26
              6 |        100        0.70       97.95
              7 |        101        0.70       98.66
              8 |         97        0.68       99.33
              9 |         96        0.67      100.00
    ------------------------------------------------


    The tabluation of the created variable shows an overrepresentation of
    zero digits in the 'hundredths' position.  This suggests around 6% of
    scores were measured with a higher precision may have been misrecorded or
    mistranscribed resulting in an incorrect precision.

Examples

    . egen units = digit(myvar)
    . egen dm2 = digit(potass), digit(-2) round(2)
    . egen dm1 = digit(potass), digit(-1) round(2)
    . egen d0  = digit(potass), digit(0) round(2)

Author

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