Introduction to Research Design and Statistics

Frequency Distributions in Stata

Examples using the hsb2 dataset.

This unit demonstrates how to produce many of the frequency distributions and plots from the previous unit, Frequency Distributions.

Frequency Distribution


use http://www.philender.com/courses/data/hsb2, clear

tabulate write


    writing |
      score |      Freq.     Percent        Cum.
------------+-----------------------------------
         31 |          4        2.00        2.00
         33 |          4        2.00        4.00
         35 |          2        1.00        5.00
         36 |          2        1.00        6.00
         37 |          3        1.50        7.50
         38 |          1        0.50        8.00
         39 |          5        2.50       10.50
         40 |          3        1.50       12.00
         41 |         10        5.00       17.00
         42 |          2        1.00       18.00
         43 |          1        0.50       18.50
         44 |         12        6.00       24.50
         45 |          1        0.50       25.00
         46 |          9        4.50       29.50
         47 |          2        1.00       30.50
         49 |         11        5.50       36.00
         50 |          2        1.00       37.00
         52 |         15        7.50       44.50
         53 |          1        0.50       45.00
         54 |         17        8.50       53.50
         55 |          3        1.50       55.00
         57 |         12        6.00       61.00
         59 |         25       12.50       73.50
         60 |          4        2.00       75.50
         61 |          4        2.00       77.50
         62 |         18        9.00       86.50
         63 |          4        2.00       88.50
         65 |         16        8.00       96.50
         67 |          7        3.50      100.00
------------+-----------------------------------
      Total |        200      100.00

Histogram with Normal Curve

histogram write, start(30) width(5) freq normal

Kernal Density Plot

kdensity write, normal width(4)

Stem-and-leaf Plot

Syntax:
stem varname [if exp] [in range] [, digits(#) [ lines(#) | width(#) ] round(#) prune ]

stem write, lines(2)

Stem-and-leaf plot for write (writing score)

  3* | 11113333
  3. | 5566777899999
  4* | 0001111111111223444444444444
  4. | 56666666667799999999999
  5* | 00222222222222222344444444444444444
  5. | 5557777777777779999999999999999999999999
  6* | 000011112222222222222222223333
  6. | 55555555555555557777777
   
stem write, lines(5)

Stem-and-leaf plot for write (writing score)

  3* | 1111
  3t | 3333
  3f | 55
  3s | 66777
  3. | 899999
  4* | 0001111111111
  4t | 223
  4f | 4444444444445
  4s | 66666666677
  4. | 99999999999
  5* | 00
  5t | 2222222222222223
  5f | 44444444444444444555
  5s | 777777777777
  5. | 9999999999999999999999999
  6* | 00001111
  6t | 2222222222222222223333
  6f | 5555555555555555
  6s | 7777777

Box Plot

graph box write



graph box write, over(prog)

Histogram with Boxplot

summarize write, d
gen f=43 /* set value a little larger than highest freq bin */
gen pmin=r(min)
gen p25=r(p25)
gen p50=r(p50)
gen p75=r(p75)
gen pmax=r(max)
gen pmean=r(mean)

two (histogram write, start(30) width(5) freq)   ///
    (rcap pmin pmax f in 1, hor bcolor(dknavy)) ///
    (rbar p25 p75 f in 1, hor bcolor(dknavy))   ///      
    (rcap p50 p50 f in 1, hor bcolor(white))    ///
    (rcapsym pmean pmean f in 1, hor msym(plus) mcolor(white)), ///
    legend(off) xtitle("Writing Score") ytitle("Frequency")
    
drop f-pmean

Using Grouped Data

To organize data into class intervals we will use the egen cut command followed by the tabulate and histogram commands.

egen clwrite = cut(write), at(30(5)70) label
 
tabulate clwrite 

    clwrite |      Freq.     Percent        Cum.
------------+-----------------------------------
        30- |          8        4.00        4.00
        35- |         13        6.50       10.50
        40- |         28       14.00       24.50
        45- |         23       11.50       36.00
        50- |         35       17.50       53.50
        55- |         40       20.00       73.50
        60- |         30       15.00       88.50
        65- |         23       11.50      100.00
------------+-----------------------------------
      Total |        200      100.00
      
codebook clwrite
 
------------------------------------------------------------------------------------------------------
clwrite                                                                                    (unlabeled)
------------------------------------------------------------------------------------------------------

                  type:  numeric (float)

                 range:  [30,65]                      units:  1
         unique values:  8                        missing .:  0/200

            tabulation:  Freq.  Value
                             8  30
                            13  35
                            28  40
                            23  45
                            35  50
                            40  55
                            30  60
                            23  65

 
histogram clwrite, freq discrete xlabel(0 "30-" 1 "35-" 2 "40-" 3 "45-" 4 "50-" 5 "55-" 6 "60-" 7  "65-")

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Phil Ender, 13Oct99