X hits on this document

PDF document

Fundamentals for the Consumer - page 16 / 31

117 views

0 shares

0 downloads

0 comments

16 / 31

88

CHAPTER 4

Simple random sampling is illustrated in the following study of mothers’strategies for influencing their children’s schooling.

:‘: :,

provided by the principal of the school.” (Baker 1986, p. 157)

mothers

and SteVensQn,

Systematic Sampling In systematic sampling every

nth

element is se-

lected from a list of all elements in the population, beginning with a randomly selected element. Thus, if there is a need to select 100 sub- jects from a population of 50,000, every nth element would correspond to every 500th subject. The first element is selected randomly. In this ample that would be some number between 1 and 500. Suppose 240 were randomly selected as a starting point. The first subject chosen for the sample would be the 240th name on a list, the next subject would be

ex-

the

74Oth,

then the

1,24Oth,

and so on until 100 subjects were selected.

Systematic sampling is virtually the same as simple random sampling. It

is certainly much

more

convenient.

There is a possible weakness in systematic sampling if the list of cases in the population is arranged in a systematic pattern. For instance, if a list of fourth-graders in a school division is arranged by and students in the classrooms are listed from high to low ability, there

cla.ssroom

is a cyclical pattern in the list (referred to

as ~tiodicit~).

If

every

nth sub

that is selected corresponds to the pattern, the sample would repre- sent only a certain level of ability and would not be representative of the

ject

population. Alphabetical lists do not usually create suitable for choosing subjects systematically.

periodicity

and are

Stratified Sampling A modification of either simple random or system- atic sampling is first to divide the population into homogeneous sub- groups and then select subjects from each subgroup, using simple ran- dom or systematic procedures, rather than the population as a whole. This is termed stratified sampling. The strata are the subgroups. Strati- fied sampling is used primarily for two reasons. First, as long the sub- groups are identified by a variable related to the dependent variable in the research (e.g., socioeconomic status in a study of achievement) and

as

results in

more

homogeneous groups, the sample will be

more

repre-

sentative of the population than if taken from the population as a whole. This result reduces error and means that a smaller sample can be chosen.

member selected.

systematic tih

sampling: the population is

of

Every

Stratified

sampling: selected from Strata

Subjects are

or

groups

of

the population.

Document info
Document views117
Page views120
Page last viewedThu Dec 08 19:42:16 UTC 2016
Pages31
Paragraphs1362
Words8405

Comments