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The content for this section is sub-divided
into the following areas:
Types of data
Top
| Foundation
tier |
Higher tier |
Notes |
Resources |
| Primary and secondary
data sources.
Qualitative and quantitative variables.
Discrete and continuous data. |
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Primary data: obtaining data
from a survey or investigation or experiment and by means of
questionnaires.
Secondary data: use of published statistics and
databases. |
N
types of data |
| Classification of data; the
need for precise definitions;
class limits and intervals. |
Implications of grouping for
loss of accuracy in presentation and calculation. |
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| Bivariate data: discrete,
continuous; ungrouped and grouped. |
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Census Data
Top
| Foundation
tier |
Higher tier |
Notes |
Resources |
| Obtaining information from a
well-defined small population.
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The definition of
'population' should be taken as the population in the study, eg a class of
pupils or all the packets of biscuits in the school shop. |
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| Obtaining information from a
large population. |
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Awareness of the National
Census. |
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Sampling
Top
| Foundation
tier |
Higher tier |
Notes |
Resources |
| Purpose of sampling;
variability between samples. |
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| Randomness. Random numbers
from tables, calculators and computers. |
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| Sampling from a well-defined
population.
Sample frame.
Simple random sampling; the condition that all
members of the population are equally likely to be included in the sample. |
Stratified sampling with one
set of categories.
Systematic sampling.
Stratified sampling with no more than two sets of
categories.
Cluster sampling and quota sampling with particular
reference to their use in conducting large scale opinion polls. |
Strengths and weaknesses of
the various sampling methods, including the dangers of convenience
sampling. The criteria used for selecting sample members in national
opinion polls: geographical area, sex, age group, social and economic
backgrounds.
Associated sources of bias.
Candidates may be required to demonstrate the process
of obtaining a random sample by using a given table of random digits.
An appreciation of the sample size selected is
required. |
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| Biased samples arising from
sampling from a wrong population or non-random choice of individual
elements.
How biased samples can occur in practice. |
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Awareness of bias in
self-selecting samples, eg telephone polling, pressure groups. |
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Obtaining data
Top
| Foundation
tier |
Higher tier |
Notes |
Resources |
| Obtaining data by counting or
measuring; accuracy of such measures.
Design and use of efficient methods of recording
data, appropriate to the purpose for which it will be used. |
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| Obtaining primary data by
questionnaire. Pilot studies and pre-testing.
Problems of design, wording, biased questions,
definitions, obtaining truthful answers.
The advantages and disadvantages of closed and open
questions.
The use of opinion scales. |
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The technique of random
response, in its simplest form, for obtaining truthful answers to
sensitive questions.
Awareness of the problems that may arise through:
identifying the population; questionnaire distribution and collection;
non-response; errors in recording answers; missing data. |
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| Obtaining data by interview.
Advantages and disadvantages of interviews compared
with written questionnaires. |
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| Obtaining data by data
logging.
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Data logging is a mechanical
or electronic method of collecting primary data by sampling at
(repetitive) set intervals and recording the data in re-usable form (list
of graph) |
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| Simulation. Use of, for
example, dice, random number tables, ICT. |
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Use of ICT methods. |
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| Using secondary data;
sources, reliability, accuracy, relevance and bias.
Difference between sample and census data. |
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Examples of sources of
secondary data are Key Data, Annual Abstract of Statistics, Monthly,
Digest of Statistics, Social Trends, Economic Trends, the Internet,
various almanacs and newspapers. |
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| Designing and obtaining data
from simple statistical experiments.
Explanatory and response variables; identification of
the variables to be investigated.
Use of a control group; use of random allocation to
experimental and control groups. |
Matched pairs of groups;
"before and after" experiments.
Identification of extraneous variables and methods of
controlling them: the need to hold extraneous variables constant for both
groups.
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Explanatory and response
variables are also referred to as independent and dependent variables
respectively. |
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| Surveys. |
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The difference between a
census and a survey. |
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The
capture/recapture method
for obtaining data. Conditions for this method to be appropriate. |
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