# Data collection

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• Created by: May Htar
• Created on: 22-03-18 10:09
Population
Whole set of items that are of interest.
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Census
Observes or measures every member of the population.
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Sample
Selection of observation taken from a subset of the population which is used to find information about the population as a whole.
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Sampling units
Individual units of a population.
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Sampling frame
Sampling units of a population that are individually named or numbered to form a list.
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Simple random sampling
Every sample of size n has an equal chance of being selected.
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Method of simple random sampling
Allocate a unique number from x to y to each member. Use a calculator or random number generator z random numbers between x and y. Select the members corresponding to these numbers.
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Systemic sampling
Required elements are chosen at regular intervals from an ordered list.
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Method of systemic sampling
E.g. if a sample of size of 20 is required from a population of 100, you would take every fifth person. Randomly select a number between 1 and 5. Start with the member corresponding to this number. Then select the member every 5th number after this.
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Stratified sampling
Population is divided into mutually exclusive strata and a random sample is taken from each.
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Method of stratified sampling
number in stratum/number in population x overall sample size = number sampled in stratum. Number the members in each strata. Use a random generator to generate the required amount of random numbers. Select the members corresponding to these number.
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Quota sampling
Interviewer or researcher selects a sample that reflects the characteristics of the whole population.
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Method of quota sampling
Divide the population into groups according to a given characteristic. The size of each group determines the proportion of the sample that should have the characteristic. Interview people, assess their groups and allocate them into appropriate quota.
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Opportunity sampling
Taking the sample from people who are available at the time the study is carried out and who fit the desired criteria.
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Method of opportunity sampling
E.g. The first 20 people you meet outside a supermarket on Monday who are carrying shopping bags.
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Quantitative variable
Variables associated with numerical observation.
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Qualitative variable
Variables associated with non-numerical observation.
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Continuous variable
Variables that can take any values in a given range.
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Discrete variable
Variables that can take only specific values in a given range.
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Daily mean temperature
Average of the hourly temperature readings during a 24-hour period.
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Daily total rainfall
Includes melted solid precipitation - amounts less than 0.05 mm are recorded as 'tr' or 'trace'
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Daily mean wind direction and wind speed
In knots, averaged over 24 hours it is also categorised according to the Beaufort scale. Mean wind directions are given as bearings and as cardinal direction
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Daily maximum gust
In knots, the highest instantaneous wind speed and direction is recorded.
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Daily maximum relative humidity
% of air saturated with water vapour. >95% give rise to misty and foggy conditions.
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Daily mean cloud cover
In 'oktas' or eighths of the sky covered by cloud.
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Daily mean visibility
In decametres, the greatest horizontal distance at which an object can be seen in daylight.
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Daily mean pressure
In hectopascals.
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Missing data
n/a or 'not available'
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## Other cards in this set

### Card 2

#### Front

Observes or measures every member of the population.

Census

### Card 3

#### Front

Selection of observation taken from a subset of the population which is used to find information about the population as a whole.

### Card 4

#### Front

Individual units of a population.

### Card 5

#### Front

Sampling units of a population that are individually named or numbered to form a list.