Sampling Method

Most research has a specific population to which the findings should apply. That may be a broad population or a narrow one in the study. Usually, the population is too large to attempt to survey all of its members. Therefore, use of sampling which aims to reduce the number of respondents brings the three main advantages: the cost is lower, data collection is faster, and since the data set is smaller it is possible to ensure homogeneity and to improve the accuracy and quality of the data (Ader et al. 2008). However, the sample should be able to represent the population to obtain the generalised results reflecting the characteristics of the whole group (Tharenou et al. 2007) and also be of sufficient size to have adequate power to detect quantitative relationships in the social sciences (Mone et al. 1996).

Sampling methods can be classified as two broad types of sampling approaches:

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1996). In probability samples, every element of the population has a known non-zero likelihood of being sampled. That is, there is no bias in the choice; each member and each household in the sampling frame has the same probability of selection. Thus, the generalisability of a study is much stronger when a probability sampling approach is adopted (Tharenou et al. 2007).Another advantage of probability sampling is that sampling error, which indicates the degree to which a sample might differ from the population, can be calculated. When inferring to the population, results are reported plus or minus the sampling error. The main types of probability sampling include simple random sampling, systematic sampling and stratified sampling. Blaxter et al. (2001) have claimed that the most widely understood probability sampling approach is

probably random sampling where every individual or object in the population of interest has an equal chance of being chosen for study.

Meanwhile, in nonprobability samples, specific elements from the population have been selected in a non-random manner. Non-randomness results mean population elements are selected on the basis of assumptions regarding the population of interest, which forms the criteria for selection because they are easy or inexpensive to reach. Therefore, nonprobability sampling approaches are usually used when a sampling frame for the population is lacked in question, or where a probabilistic approach is not judged to be necessary. Unlike probability sampling techniques, sampling error remains unknown in nonprobability sampling. In other words, these conditions provide limited information about the relationship between sample and population, making it difficult to extrapolate from the sample to the population. Nonprobability sampling methods include

convenience sampling, judgment sampling, quota sampling and snowball sampling. According to Blaxter et al. (2001), market researchers commonly use a quota sampling approach with targets for the numbers they have to interview with different socio- demographic characteristics.

4.6.1 Sampling frame

The sampling frame is defined as a list or set of directions for identifying the target population by Malhotra (1999). Bradly (1999) has divided the internet sampling frame

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into internal and external. In terms of the internal, respondents are selected on the internet itself either as website visitors or among e-mail address listings. In cases of the external, respondents are chosen elsewhere such as from panels or from paper

directories. These respondents are then invited to the internet for a data collection.

4.6.2 Survey sampling approach

Since the number of online grocery shoppers is relatively small compared to the general population of internet shoppers, it is difficult to detect the target samples. The data presented in this study were collected via an online (web-based) survey using self- administered questionnaire. The target population consists of UK consumers who have had an experience of online grocery shopping and adults, over 18 years of age. The questionnaire, firstly, was distributed to the individual respondents by the use of e-mail lists administered by a market research firm named ‘DataCorp’. Total 600,000 e-mails were delivered as initial mail of 300,000 with a reminder mail of 300,000 over two- week period beginning on Monday 18th April 2011. As a result, only 13 responses were collected. Then, the questionnaire was reorganised to make a look much shorter and simpler so that more people are to participate to the survey. The number of pages was reduced from 12 to 6 pages rearranging questions from one question per page to at least three questions per page. In addition, some similar measures were combined and few measures thought to be unnecessary were removed to reduce the time taken to complete the questionnaire. It finally took 3-5 minutes to complete. Another e-mail delivery was attempted with newly amended version of questionnaire for another two weeks.

Unfortunately, there were very little 8 replies. The e-mail campaign with total 21 responses was judged to be failed to generate a sufficient sample.

A new approach which can generate an acceptable sample size and a representative sample of online grocery shoppers was needed. Advertising on the web was adopted to reach a substantial sample using the same questionnaire. However, this time an

incentive in the form of supermarket giftcards by a prize draw were offered in order to encourage more people to join in the survey. Each prize was allocated to the randomly selected eight respondents. The detail of prizes shows below:

81 First prize (1 person) - £100 supermarket giftcard Second prize (2 people) – £50 supermarket giftcard Third prize (5 people) – £10 supermarket giftcard

At first, advertising was posted on the 6 different consumer forums which are related to the issues of UK business and consumer information. Secondly, advertising was also accomplished through ‘Gumtree’ that is an extensive network of online classifieds and community websites. Thirdly, advertising linked to Social Media such as ‘Facebook’ was tried because advertising with Facebook Adverts is allowed to reach the exact target population effectively using keywords included location, age and interests. Specifically, this advert has targeted 65,280 users who are categorised into age 18 and older living in the UK, and who are interested in advertising, food shopping, internet shopping, online grocery shoppers, research, supermarket or survey. There was an option to choose a pay method between CPC (cost per click) and CPM (cost per 1000 impressions). In case of this research, it would be more important to give awareness about the survey to as many people as possible rather than simply get click through to an advert if daily budget was set the same. Therefore, CPM was considered more effective to promote this survey. The advert on the Facebook website was showed on the right hand side of the main page of each user who is matched for the criteria of this survey, as depicted in Figure 4.1.

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Collecting responses were operated for approximately three weeks from 3rd to 22nd July 2011. The draw result was announced on the first page of the questionnaire on the web and, at the same time, confirmation emails were sent to all winners on 23rd July 2011. This approach has generated a sample of 351, which are an acceptable number of responses. Subsequently, the survey yielded total 372 valid responses.