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Slide 2

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This data is numerical. This means the data uses numbers.
e.g. the price of an object
Age
This data isn't numerical. This means it doesn't use numbers.
e.g. colours
This data is collected by the person who will use the information.
e.g. results of a questionnaire
taking measurements
This data is not collected by the person who will use the information.
e.g. obtained from published statistics/databases
data found in textbooks or on the internet…read more

Slide 3

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The complete set of people/objects that the information is collected about.
A list of all the items of the population.
When data is collected from every person or about every object.
Anything that distorts data so it is not a fair representation. This makes results
unreliable.
Information is usually taken from a small part of the population. This is a sample
of the population. It is easier and cheaper to take a sample rather than a
census.…read more

Slide 4

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Every member of the population has an equal chance of being selected.
Random samples can be found using:
1. Writing numbers on paper and choosing a number at random
2. Random number tables
3. Random number generator on scientific calculators
Every member of the sample is chosen at regular intervals
from a list.
To find a start point, a random number needs to be chosen
to remove bias, however the order in the list might have
been deliberately made instead of having no order.…read more

Slide 5

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This is when someone is conducting a questionnaire and asks a certain number of
people. This can be biased if the person chooses who to ask or if people don't
participate.
If a population is divided into groups, the groups must be fairly represented in the
sample. The number chosen from each group is proportional to the group size.
This sampling method is often used in market research as it is very cheap but
unreliable. The interviewer asks certain people that must be of a certain type. This
could be age, sex or social class.
The population is divided into smaller groups called clusters. One or more of the
clusters are chosen and every member chosen is used. This is also very cheap but
doesn't remove all bias.…read more

Slide 6

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A group of people are chosen at random to take part in a test, for example,
patients for a new drug. The population is then split in two at random. Both groups
think that they are getting the drug, however, only one group receives the drug.
The group without the drug is called the control group. There may be more than
two groups.
This can be used to see if something has an effect or if the problem is to do with
the person.…read more

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