The document discusses the importance and benefits of sampling over a census for research purposes. It notes that sampling saves time and money compared to a census. Additionally, a sample may be more accurate than a census due to limitations in resources and risks of introducing unpopular actions to an entire market. The document also emphasizes that both sampling design and sample size are important considerations, as an inappropriate design will not allow findings to be generalized even with a large sample, and an inadequate sample size cannot meet study objectives. It provides some general guidelines for appropriate sample sizes.

1. IMPORTANCE OF SAMPLING
 A sample saves money and time.
 Compare a sample versus a census:
 Far greater speed in completing a 5%
randomly selected sample, as opposed to
increasingly larger surveys (10%, 20%, etc.)
 Few census designs would satisfy the value of
information constraint in marketing research.
 Sample size is directly related to the cost
of a study, the more representative the
sample, the lower the sample size
needed.

2. IMPORTANCE OF SAMPLING
 A sample may be more accurate than a
census.
 A census requires enormous numbers of
interviewers, supervisors of interviewers, and
people for data entry. There is limited supply of
qualified labor available for any research
purpose, which minimize sampling error.
 A sample is better in the event that the study
results in the destruction or contamination of
the element sampled.
 You don't want to risk the potential disadvantages
of introducing a unpopular marketing action
(advertisement, product, or price) to an entire
market.

3. IMPORTANCE OF SAMPLING
DESIGN AND SAMPLE SIZE
Sampling decisions should consider
both sampling design and sample size,
because
If the sampling design is inappropriate,
a large sample size will not allow the
findings to be generalized.
If the sample size is inadequate, no
sampling design, can be useful in
meeting the objectives of the study

4. IMPORTANCE OF SAMPLING
DESIGN AND SAMPLE SIZE
 There are some general rules regarding sample
size
 Sample sizes larger than 30 and less than 500 are
appropriate for most research.
 Where samples consists of subsets like male/
female, rural/ urban etc, it is appropriate to
ensure a minimum sample size of 30 for each
subset
 In multivariate research, the sample size should
be several times as large as the number of
variables in the study
 For simple experimental research with tight
controls, a sample size of 10 to 20 is adequate.

5. Sample Size Determination for a Mean:
Interval or Ratio Questionnaire Items
Where…
n = the sample size
z = standard error associated with the chosen level of
confidence
s = variability indicated by an estimated standard deviation
e = acceptable error
2
22
e
zs
n =

6. Sample Size Determination for a Mean:
Interval or Ratio Questionnaire Items
Where…
n = the sample size
z = standard error associated with the chosen level of
confidence
s = variability indicated by an estimated standard deviation
e = acceptable error
2
22
e
zs
n =