Sta220 - Statistics
Mr. Smith
Room 310
Class #10
Section 3.7
3.7 Random Sampling
If n elements are selected from a population in such a way that
every set of n elements in the population has an equal probability
of being selected, then the n elements said to be a random
sample.
A random sample is likely to be the representative of
the population that it is selected from.
Most researchers rely on random-number generators to
automatically generate a random sample.
Random samples are a sampling procedure that will likely
lead to the creation of a representative sample.
Generation Random Numbers
www.random.org
TI-84
Go to Math-> PRB-> randInt(
Problem
Suppose you wish to randomly sample five households from a
population of 100,000 households.
a) How many different samples can be selected?
b) Use a random-number generator to select a random sample. (Table
3.7)
a) How many different samples can be selected?
Since we want to select 5 households from 100,000, we apply the
combinations rule.
n=5
N = 100,000
𝑁
𝑛
=
100,000
5
=
100000!
5!99,995!
= 8.33 x 1022
Calculator:
To use the combination rule:
1) Punch in the top number
2) Go to Math->PRB->nCr(#3)->enter
3) Punch in the bottom number
Ex.) 100000 nCr 5 =
8.332500029e22
b) Use a random-number generator to select a random sample. (Table
3.7)
Once all the number had been generated on paper would arbitrarily
select a starting number, say, the random number appearing in the
third row, second column. This number should be 48,360. Then we
proceed down the second column to obtain the remaining four random
numbers.
48,360 93,093 39,975 6,907 72,905
A blind study is a study where the subjects on which the
experiment is being conducted do not know into which
experimental group they have been placed.
Important Dates
1) Assignment 3.6 due 03/17/14 (11:00 p.m.)
2) Assignment 3.7 (Notes Thursday) due by 3/17/14 (11:00 p.m.)
3) Ch. 3 Review Quiz and Ch. 3 Homework Review Due by 3/19/14
(11:00 p.m.) *ACT Tuesday
4) Unit 2 Test 3/21/14