Sampling TechniquesSnowball Sampling & Purposive Sampling

Prepared by :

NAMA PENUH NOMBOR MATRIK

SARIAH BINTI MEGAT YACOB D20111048844

CHRISTINA ANAK RINGGIT D20111048850

SAIDATUL NADHRAH BINTI ABDULLAH D201111048855

DYGKU NURUL HAFIZAH BINTI AWG MUSTAPHA D20111048856

MUHAMMAD FIQRI BIN MUSTAFFA D20111048884

NAMA PENUH NOMBOR MATRIK

MUHAMMAD FIQRI BIN MUSTAFFA D20111048884

SARIAH BINTI MEGAT YACOB D20111048844

DYGKU NURUL HAFIZAH BINTI AWG MUSTAPHA D20111048856

CHRISTINA ANAK RINGGIT D20111048850

SAIDATUL NADHRAH BINTI ABDULLAH D201111048855

Snowball Sampling

DEFINITION

Snowball sampling is a

NON-PROBABILITY sampling technique that is used by researchers toIDENTIFY potential subjects in studies where SUBJECTS are HARD to

LOCATE.

Types of SNOWBALL SAMPLING

TYPES OF SNOWBALL SAMPLING

LINEAR TYPE

Exponential Non-Discriminative Snowball Sampling

Exponential Discriminative Snowball Sampling

ADVANTAGES & DISADVANTAGESSNOWBALL SAMPLING

ADVANTAGES OF SNOWBALL SAMPLING

1. LOCATE HIDDEN POPULATIONSIt is possible for the surveyors to include people in the survey that they would not have known.

2. LOCATING PEOPLE OF A SPECIFIC POPULATIONThere is no lists or other obvious sources for locating members of the population of specific interest.

3. CHEAPThe process is cheap, simple and cost-efficient. This sampling technique needs little planning and fewer workforce compared to other sampling techniques.

Community Bias

Not Random

Vague Overall

Sampling Size

Wrong Archorin

g

DISADVANTAGE OF SNOWBALL SAMPLING

1. COMMUNITY BIASThe first participants will have strong impact on the sample. Snowball sampling is inexact, and can produce varied and inaccurate results. The method is heavily reliant on the skill of the individual conducting the actual sampling, and that individual’s ability to vertically network and find an appropriate sample. To be successful requires previous contacts within the target areas, and the ability to keep the information flow going throughout the target group.

2. NOT RANDOMSnowball sampling contradicts many of the assumptions supporting conventional notions of random selection and representativeness. However, Social systems are beyond researcher’s ability to recruit randomly. Snowball sampling is inevitable in social systems.

3. VAGUE OVERALL SAMPLING SIZEThere is no way to know the total size of the overall population.

4. WRONG ARCHORINGAnother disadvantage of snowball sampling is the lack of definite knowledge as to whether or not the sample is an accurate reading of the target population. By targeting only a few select people, it is not always indicative of the actual trends within the result group. Identifying the appropriate person to conduct the sampling, as well as locating the correct targets is a time consuming process which renders the benefits only slightly outweighing the costs.

Purposive Sampling

Definition

A type of non probability sampling where the researcher consciously selects particular elements or subjects for addition in a study so as to

make sure that the elements will have certain characteristics pertinent to the study.

It normally targets a particular group of people.

A purposive sample is a non-representative subset of some larger population, and is constructed to serve a very specific

need or purpose.

Definition

Selection of individuals with specific characteristics.

One might:

1.Request certain individuals within a population (e.g., ask for an adult male in the household in a telephone survey)

Definition

Restrict the sampling to certain audiences (e.g., select a sample from readers of Popular Mechanics)

Specify a need for individuals with certain characteristics (e.g., solicit with ads).

Definition

VIDEO PURPOSIVE SAMPLING

ADVANTAGES & DISADVANTAGESPURPOSIVE SAMPLING

ADVANTAGES

• Less costly and less time consuming

• Ensures proper representation

• Prevents unnecessary and irrelevant items entering into sample per chance

• Ensures intensive study of the selected items.

• Gives better results if the investigator is unbiased & has the capacity of keen observation and sound judgment.

DISADVANTAGES• No equal chance for all the items of the universe being

included in the sample.

• No possibility of having any idea about the degree of accuracy achieved in the investigation conducted

• Enough space for bias or prejudices of the investigate to play and influence the selection.

• Not suitable for the large samples where the size of both universe and the sample considerably large.

• No possibility of calculating the sample error the idea of which is based on the mathematical concepts which are no applicable to non random methods of sampling.

Example of Snowball Sampling & Purposive Sampling

Example of Snowball Sampling

UseUse when you do not have access to sufficient people with the characteristics you are seeking.

MethodFind people to study.Ask them to refer you other people who fit your study requirements, then follow up with these new people.Repeat this method of requesting referrals until you have studied enough people.

Example of Snowball Sampling

ExampleA researcher is studying environmental engineers but can only find five. She asks these engineers if they know any more. They give her several further referrals, who in turn provide additional contacts. In this way, she manages to contact sufficient engineers.

Example of Snowball Sampling

DiscussionThe 'snowball' effect occurs as referrals multiply at each step. For example if you got two referrals from each person, then starting from two people get four more, then eight, sixteen and so on.Snowball sampling uses a method beloved by sales people, where customer referrals to new prospects have particular value as the relationship of trust and obligation between the identified person and the referrer makes it more likely that the new person will make a purchase.The way that the sample is chosen by target people makes it liable to various forms of bias. People tend to associate not only with people with the same study selection characteristic but also with other characteristics. This increases the chance of correlations being found in the study that do not apply to the generalized wider population.

Example of Snowball Sampling

The need to get the person to give you a referral also means that the researcher has to form a relationship with the person and be nice to them. This can change the study results as affective biases in both the researcher and the target person change how they think and behave.With care in selection (you do not have to use every referral) and avoiding personal bias, snowball sampling can still be a useful method, particularly if you have no other way of reaching the target population.Snowball sampling is also known as chain sampling, chain-referral sampling or referral sampling.

Example of Purposive Sampling

UseUse when you want to access a particular subset of people.

MethodWhen taking the sample, reject people who do not fit a particular profile.

Example of Purposive Sampling

ExampleA researcher wants to get opinions from non-working mothers. They go around an area knocking on doors during the day when children are likely to be at school. They ask to speak to the 'woman of the house. Their first questions are then about whether there are children and whether the woman has a day job. .

Example of Purposive Sampling

DiscussionPurposive sampling starts with a purpose in mind and the sample is thus selected to include people of interest and exclude those who do not suit the purpose.This method is popular with newspapers and magazines which want to make a particular point. This is also true for marketing researchers who are seeking support for their product. They typically start with people in the street, first approaching only 'likely suspects' and then starting with questions that reject people who do not suit.Purposive sampling is non-probability and hence can be subject to bias and error.

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