random

random sampling

select a random sample from a population

population <- 1:100                                    # list of candidates, 1 ... 100
sample.size <- 10                                      # size of desired sample
samp <- sample(population, size=sample.size)           # desired random sample
sort(samp)                                             # sorted sample           
##  [1]  1 19 36 52 76 78 85 91 98 99

random assignment

randomly assign participants to groups

sample.size <- 10
n.groups <- 3
n.population <- n.groups * sample.size
population <- 1:n.population                           # list of candidates, 1 ... 30
samp <- sample(population, size=n.population)          # permute the list
samp <- matrix(samp, nrow=n.groups)                    # format as matrix
samp                                                   # each row is a group
##      [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
## [1,]   26   10    7   16   14   22    8    6   11    21
## [2,]   30    3   13    1    9    5   18   23   27    15
## [3,]   28   12    4   24   25   19   17   29    2    20

exercises

  1. Select a random sample of 5 students from the 24 Stat 204 students in this room. Do it again.

SOLUTION:

  1. Randomly assign the 24 Stat 204 students in this room to two groups of 12 students each. Do it again.

SOLUTION: