Data Sampling and Questionnaires

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Data Sampling and Questionnaires

Sampling is the process of looking at a small selection of people/objects from a wider population in order to learn new information about that population. There are many ways of sampling data, but the main methods we look at are random sampling and questionnaires.

Make sure you are happy with the following topics before continuing.

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Data Sampling

Data sampling is when you use a smaller sample of a large group to in order to represent the whole sample.

Example: Suppose we wanted to know the reading habits of people living in the UK.

In reality, it would be better to ask every single member of the population – this would be VERY reliable, but VERY expensive, and time consuming.

A positive of data sampling is that it is less time-consuming,

A negative of data sampling is that it might be less reliable, and possibly biased. For example, if you only asked people who were leaving a library, then all your results may be much higher than otherwise.

The aim is to make a sample as representative of the whole population as possible (i.e. reduce the amount of bias).

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Random Sampling

Random sampling is the best way to avoid any sort of bias.

For instance, in biological studies where biologists want to determine the number of plant species in a large wide open area, they select random spaces to sample by plotting the area on a grid and using a random number generator to select coordinates, which tells them which area to sample.

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Questionnaires

The purpose of a questionnaire is to help extract the information you require, whilst avoiding bias and giving people the opportunity to give a whole range of possible answers. Constructing questionnaires in the correct way and being able to spot poor questionnaires is what you will be asked questions on.

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Example: Questionnaires

Phillipa has designed a questionnaire to learn about TV-watching habits. She intends to put this questionnaire to $30$ of her classmates.

a) Find $2$ problems with this questionnaire and explain your answer.

b) Redesign the questionnaire so that it is more likely to collect meaningful data.

[4 marks]

a) There are more than just two problems with this, so we’ll go through them all.

Time frame – The question must include a time frame, per day, per week, per month?

Options – There are no options for someone who watches no TV at all, or someone who watches more than $20$ hours of TV.

Overlapping options – There is a crossover between the options – if I watch $5$ hours of TV, then should I tick the first box or the second?

Bias – Only people from one class are being asked, this doesn’t represent the wider population and ultimately may result in biased data.

Clarity – It isn’t clear whether the hours spent watching TV includes time spent watching online streaming services on other types of devices such as phones and computers.

b) Redesigning the questionnaire will mean addressing all of the points listed above. The following questionnaire is just an example.

Additionally, there are a couple of other important things to consider when writing questionnaires.

Leading questions – e.g. “how amazing was the last Star Wars film?” – this could pressure the person into answering positively, adding Bias into the answer.

Personal questions – e.g “do you have a criminal record?” might make the person feel uncomfortable and not answer truthfully.

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Data Sampling and Questionnaires Example Questions

The first criticism is that Tilly’s question is a leading question – she leads people into agreeing with her opinion that the new government will be a disaster.

The second criticism is that there are not enough options – somebody might have no opinion on the matter, or they could be neutral about it.

Here is an example of an improved question:

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The first criticism is that there are crossovers between the options – if I spend $£30$ on food each week I won’t know whether to tick the first or the second box.

The second criticism is that there are not enough options – there is no suitable box to tick for someone who spends more than $£120$ on food every week.

Because he is only asking people at the end of his street, Saru will probably get answers which are lower than if he asked this question at the end of a different street where the houses were bigger/more expensive, therefore his survey will probably be biased.

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(a)

• although it does specify the time frame the results will depend on the time of day the person is completing the questionnaire.
• overlapping response boxes. Someone who has taken $5000$ steps could tick two of the responses.

(b)

Here the question is framed better as it is independent of when the form is completed and asks for a value people are more likely to know the answer to on the spot. Also the response boxes no longer overlap. Other improvements could include a response box for those who do not know.

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There needs to be some time frame referenced in the question otherwise people will answer over varying time frames. Someone could respond with the amount the receive per week and someone else could give their pocket money amount over the course over year.

Including a option for zero and having no overlapping response boxes is also important.

The new questionnaire should look something like:

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The original questionnaire has very subjective answer that are qualitative rather than quantitative.

A better questionnaire has the options with a specified number of average visits over a certain time frame. This will gather much more useful data for the manager of the cinema.

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Data Sampling and Questionnaires Worksheet and Example Questions

(NEW) Data and Questionnaires Exam Style Questions - MME

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Data Sampling and Questionnaires Drill Questions

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Sampling Data and Frequency Polygons - Drill Questions

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