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daily mean temperature
measured in C
average of the hourly temperature readings measured during a 24-hour period
daily total rainfall
measured in mm (to 1 d.p.)
includes rain, snow and hail (melted)
amounts less than 0.05mm are recorded as ‘tr‘ (trace)
daily total sunshine
measured in hours (to the nearest tenth of an hour)
daily maximum relative humidity
the amount of water vapour in the air
measured as a percentage of maximum water vapour that could be in the air
daily mean windspeed (& direction)
measured in knots (1 knot = 1.15 mph)
direction is measured in degrees (to the nearest 10)
daily maximum gust (& direction)
measured in knots (1 knot = 1.15 mph)*
direction is measured in degrees (from the north)
*beaufort conversion
daily mean visibility
the greatest horizontal distance at which an object can be seen in daylight
measured in dm (decameters/10m)
daily mean pressure
measured in hectopascals (hPa)
small range (~980 to 1035)
daily mean cloud cover
measured in oktas (how many eighths of the sky is covered in clouds)
population
a whole set of items that are of interest
census
observes or measures every member of a population
benefits and drawbacks of a census
it should give a completely accurate result
time consuming and expensive
cannot be used when the testing process destroys the item
sample
a selection of observations taken from a subset of the population
used to find out about the population as a whole
benefits and drawbacks of a sample
less time consuming and expensive than a census
the data may not be as accurate
the sample may not be large enough to give accurate information about a small sub-groups of the population
sampling unit
individual units of a population
sampling frame
a list of sampling units that are individually named or numbered
simple random sample
random sampling method
each unit is allocated a unique number and numbers are selected randomly
numbers can be generated randomly (using a computer) or ‘drawn from a hat’
benefits and drawbacks of simple random sampling
free of bias
each sampling has a known and equal chance of selection
not suitable when the population/sample size is large, as it is potentially time consuming, disruptive and expensive
a sampling frame is needed
systemic sampling
random sampling method
required elements are chosen at regular intervals from an ordered list
the first item is chosen randomly, the rest chosen at regular intervals from the first (e.g. every 5 items)
benefits and drawbacks of systemic sampling
simple and quick to use
suitable for large populations/samples
a sampling frame is needed
can introduce bias if sampling frame is not random
stratified sampling
random sampling method
the population is divided into mutually exclusive strata (e.g under 18s and over 18s) and a simple random sample is taken from each
the number of samples taken from each strata must be proportional to the population
benefits and drawbacks of stratified sampling
sample accurately reflects the population structure
guarantees proportional representation of groups within a population
population must be clearly classified into distinct strata
selection within each stratum has the same disadvantages as simple random
quota sampling
non-random sampling
the population is divided into groups (quotas) according to a given characteristic
the interviewer meets people, assesses their group and allocates them into the appropriate quota
benefits and drawbacks of quota sampling
allows a small sample to still be representative of the population
no sampling frame required
quick, easy and inexpensive
non-random sampling can introduce bias
opportunity sampling
non-random sampling method
consists of taking a sample from people who are available at the time, who fit the criteria
benefits and drawbacks of opportunity sampling
inexpensive and easy to carry out
unlikely to provide a representative sample
highly dependent on individual researcher
quantitative data
data associated with numerical observations
qualitative data
data associated with non-numerical observations
continuous variable
a variable that can take any value in a given range
discrete variable
a variable that can only take specific values in a given range
frequency density
frequency ÷ class width
