Stats Flashcards
Discrete data is:
Data with a specific value e.g. age or shoes size
Continuous data is:
Data that can have any value within a specific range e.g. foot length (time can be either)
Population is:
Whole set of the thing you’re interested in
Sample is:
Subset of the thing you’re interested in
Pros and cons of sample (instead of population)
Pros: quicker, faster, cheaper. Cons: might not represent full population, may introduce bias
Sampling frame is:
list of all members of a population
Population parameter is:
numerical value describing a characteristic of the population
Random sampling
Every member of a group has an equal chance of being selected
Pros of random sampling
Free of bias, easy & cheap for small samples & populations. Each sampling unit has a known an equal chance of selection.
cons of random sampling
Not suitable for large samples& populations. sampling frame needed
Systematic sampling
The required elements are chosen at regular intervals from an ordered list
stratified sampling
The population is divided into mutually exclusive strata (e.g men and women), random sample is taken from each
advantages of systematic sampling
Simple and quick to use. suitable for large samples and large populations
advantages of stratified sampling
Sample accurately reflect population structure. proportional representation of group with population
disadvantages of systematic sampling
Sampling frame is needed. bias introduced if sampling frame is not random
non-random sampling: quota sampling
An interviewer or research selects a sample that reflects the characteristics of the whole population
non-random sampling: opportunity sampling
taking the sample from people who are available at the time of the study is carried out and who fit the criteria you’re looking for
advantages of quota sampling
Allows a small sample to still be representative of the population. no sampling frame needed. quick, easy & inexpensive allows for easy comparison between different different groups with an a population
disadvantages of quota sampling
Non-random sampling can introduce bias. population must be divided into groups which can be costly or inaccurate, increasing scope of study increases number of groups which adds time and expense, non responses are not recorded as such
advantages of opportunity sampling
Easy to carry out, inexpensive
disadvantages of opportunity sampling
Unlikely to provide a representative sample, highly dependent on individual researcher
daily mean temperature
measured in C, average hourly temperature readings during 24h period
Daily total rainfall
Including snow and hail (melted before inclusion), amounts less than .05mm recorded as tr or trace
Daily total sunshine
recorded to nearest tenth of an hour
Daily mean wind direction & windspeed
in knots, averaged over 24hrs from midnight to midnight. wind direction given as bearings and compass directions. categorised in Beaufort scale
Daily maximum gust
in knots, highest instantaneous windspeed recorded, direction is also recorded
Daily maximum relative humidity
given as percentage of air saturation with water vapour, about 95% rise to misty and foggy conditions
Daily mean cloud cover
measured in ‘oktas’ or eighths of sky covered by cloud
Daily mean visibility
measured in decameters (Dm), greatest horizontal distance which an object can be seen in daylight
Mean
the average calculated using formula: Sum of X / number of values
Mode
value that occurs the most often in a data set
Median
middle value when data is in order of size
