sampling dr majed el-farra1 selecting samples chapter 6

sampling Dr Majed El-Farra 1

Selecting samples

Chapter 6


Meeting objectives

1. Understand the need and importance of sampling in business and management research.

2. Be aware of a range of probability and non-probability sampling techniques.

3. Be aware of how to select the write research sample.


Sample provide alternatives to census when: importance:

1. It would be impractical to survey the entire population.

2. You have limited budget to survey the entire population.

3. Limited time available.4. You need quick results.


Sampling techniques

Probability or representative sampling Non-probability or judgmental

sampling. Probability sampling: the chance or

probability of each case being selected from the population is known and is usually equal for all cases.

Non-probability sampling: the opposite.


Probability sampling

It is associated with survey-based research where you need to make inferences/conclusions from your sample about a population to answer your research question or to meet your objectives.


Steps of designing probability sampling.

1. Identify a suitable sampling frame based on your research question.

2. Decide on a suitable sample size.3. Select the most appropriate sampling

technique and select the sample.4. Check that the sample is

representative of the population.


Identifying a suitable sampling frame The sampling frame for probability sample

is a complete list of all the population cases.

Examples on sampling frame: teamwork activity:

1. Leadership style of Gaza’s managers in the private sector.

2. Constraints of scientific research at IUG faculty of commerce: Academics viewpoint.

3. Internal constraints of industrial development in the Gaza Strip.


Factors govern sample size

1. The confidence you need in data.2. The margin of error that you can

tolerate.3. The type of analysis that you are

going to undertake.4. The size of total population.


Views on Sample size The economists

believe that sample size of 30 would be relevant to many cases.

Researchers normally work to a 95% level certainty. The margin error is 5%.

Pop. 5% margin eror

100 79

150 108

300 168

500 21

1000 278

2000 322

5000 357

10000 370


Reasons for non-response

1. Refusal to respond.2. Ineligibility to respond. Does not

meet research requirements.3. Inability to locate respondent.4. Respondent located but unable


Select the most appropriate sampling technique and select the sample.

Simple sample Systematic Stratified sample Cluster Multi-stage


Simple random sample Select the sample at a random from the

sampling frame. How to select:1. Number each of the cases in your sampling

frame (0,1,2,..).2. Select cases using random number. Methods: sampling with replacement and

without replacement. Random selection reduce bias. Random sample is used when you can list

the entire population.


Systematic sampling Selecting the sample at regular intervals

from the sampling frame. Selection steps:1. Number each of the cases with unique

number.2. Select the first case using a random

number.3. Calculate the sampling fraction: sample

size/population size4. Select the subsequent cases

systematically.


Stratifies random sampling

steps1. You divide the population into 2 or

more strata based on one or a number of attributes.

2. Random sample is drawn (simple or systematic) from each strata.


Cluster sampling You divide the population into

discrete/separate groups prior to sampling. The sampling frame is the complete list of

clusters rather than complete list of cases within the population.

You select few clusters. Used when you undertake an interview

based research and you have limited resources.

Ex. Conducting research on the behavior in of visa card clients in the Gaza Strip.


Multi-stage sampling or multi-stage cluster sampling Used when the population geographically dispersed,

and face to face contact is needed. Steps: Phase one:1. Choose sampling frame of relevant discrete groups.2. Number each group with a unique number (0,1)3. Select randomly a small sample of relevant discrete

groups using some form of random sampling Phase two:From the relevant discrete groups choose a sampling

frame and continue the steps as mentioned above. Phase three: repeat phase 2 if necessary.


Non-probability sampling In the exploratory stages non-probability

sampling may be the most practical, using pilot survey.

Sampling techniques:1. Quota2. Purposive3. Snowball4. Self-selection5. convenience


Non-probability sampling Quota Alternative to stratified sample. When is it used?1. Cost constrained2. Data needed quickly Steps of designing quota sampling:1. Divide the population into specific groups.2. Calculate a quota for each group based on relevant and

available data.3. Collect data from defined numbers. Quota is used in market research surveys, usually include

measures of age, gender, socioeconomic status. It can often produce a good results, but you cannot

measure the level of certainty.


Non-probability sampling Purposive or judgmental:Usually used with small samples, or used with

researchers following the grounded theory. Purposive sampling strategies:1. Focuses on extreme cases e.g., most success

companies. This enables you understand more typical cases.

2. Heterogeneous or maximum variation sampling. You should identify the diverse characteristics prior selection.

3. Homogeneous: focus on one particular subgroup, all sample members are similar.


Non-probability sampling SnowballUsed when it is difficult to identify members of

desired population. Respondents are most likely identify other potential respondents.

There is a problem in representativeness.e.g. knowing how CEO succeeded and reach

such high rank.We start with one CEO and he helps in identify

others to meet and others identify others and so one.


Non-probability sampling

Self-selectionWhen you allow individuals to identify

their desire/willingness to take part in the research by informing them with your research problem and objectives. Data will be collected from individuals who express their interest to participate.


Non-probability sampling

Convenience/ haphazard sampling.Involves selecting haphazardly those

cases that are easiest to obtain. Example: standing at the uni. Campus

and ask students you meet to fill a questionnaire and you keep doing so tell you get the sample size.


Group work

Simple sample Systematic Stratified sample Cluster Multi-stageTwo groups will work on these samples. They

should draw working examples how to use these samples in reality. Theses samples will be divided between the groups.


Group work

Sampling techniques:1. Quota2. Purposive3. Snowball4. Self-selection5. ConvenienceTwo groups will work on these samples. They

should draw working examples how to use these samples in reality. Theses samples will be divided between the groups.

sampling dr majed el-farra1 selecting samples chapter 6

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