Page 61 - DMGT408DMGT203_Marketing Management

Marketing Management/Essentials of Marketing

Notes
Example: If Sahara Airlines conducts a survey, should the sampling unit be business
travellers, vacation travellers, or both? Should travellers under age 30 years be interviewed?
Interviewing the correct target market or the potential target market is basic to the validity of
research.
Investigating all members of a population is virtually impossible as the time and resources
available for research are limited. However, the research must reflect the universe (the entire
target population). Researchers obtain the needed amount of data through sampling. They
select a limited number of units (sample) that they expect to represent the characteristics of a
population. As a rule, the size of a sample must be large enough to achieve accuracy and
stability. Larger sample size ensures more reliable results. Reliability though, can be achieved
even with very small samples, such as 1% of the population. There are two broad types of
sampling techniques: random probability samples and non-probability samples.

Table 2.1: Probability and Non-probability Samples

Probability sample
Simple random sample Every member of the population has an equal chance of being selected.
Stratified random The population is divided into mutually exclusive groups (such as gender,
sample age group), and random samples are drawn from each group.
Cluster or area sample The population is divided into mutually exclusive groups (such as city,
village) and the researcher draws a sample of the groups to be interviewed.
Non-probability sample
Convenience sample The researcher selects the most accessible population members to
interview and obtain information (such as shoppers in a departmental
store).
Judgement sample The researcher uses her/his judgement to choose population members
who are good prospects for accurate information (such as doctors).
Quota sample The researcher finds and interviews a predetermined number of
respondents in each of several categories (such as 50 males and 50 females).

Random Probability Sampling

The greatest accuracy is obtained from random probability samples because all units in a
population have a known and equal chance of being selected. For example, in a lottery, when all
the ticket numbers are mixed up, each number should have an equal probability of being
selected. The difficulty with this method is that every unit (individual, or family, etc.) must be
known, listed, and numbered to have equal chance of being selected. The task is often prohibitively
expensive with customers of widely distributed products. Researchers use stratified sampling
by dividing the population of interest into groups, or strata, based on some common characteristic
and then conduct a random sample within each group. Area sampling is a variation of stratified
sampling wherein researchers divide the population into geographic areas and select the units
within the selected areas for a random sample.
Non-probability sampling: This sampling method is easier, less expensive and time consuming
than probability sampling and for this reason, researchers use it extensively. This method involves
the researcher’s personal judgement and elements of the population do not have a known chance
of being selected, so there is no guarantee the sample is representative and the researchers cannot
be as confident in the validity of the responses. Most research situations in marketing or advertising
require general measures of the data and non-probability method of interviewing suffices to find
out the shopping preferences, customers’ attitudes, image perceptions, etc. Non-probability
sampling techniques include quota sampling, judgement sampling, and convenience sampling.

54 LOVELY PROFESSIONAL UNIVERSITY