alevel maths( statistics)

Population

The whole set of items that are of interest

Sample

A subset of the population intended to represent the whole population

Advantages

Cheaper, quicker, less data to process

Disadvantages:

Data may not be accurate

Data may not be large enough to represent small sub groups

What variables are included in the Edexcel Large Data Set, and what are their units/meanings?

Variable	Unit / Meaning
Daily mean temperature	°C
Daily total rainfall	mm
Daily total sunshine	hours measures sunshine to the nearest hour
Daily mean windspeed	knots (kn)
Daily mean windspeed	Also classified using Beaufort scale
Daily maximum gust	knots (kn)highest instantaneous wind speed
Daily maximum relative humidity	%percentage of air saturation with water vapour
Daily mean visibility	metres (m) how far can be seen to the horizon during daylight
Daily mean pressure	hPa (hectopascals)
Daily mean total cloud cover	oktas number of eighths of the sky covered by cloud
Wind direction	Direction the wind comes from (e.g. N, NE, SW)

Beaufort	Description	Wind speed
0	Calm	< 1 kn
1-3	Light	1-10 kn
4	Moderate	11-16 kn
5	Fresh	17-21 kn

Sampling frame

The list of all the members of the population from which you can select your sample e.g a list of residents

Sampling unit

Each individual thing in a population that can be sampled

Census

Data collected from the entire population

Advantages: should give a completely accurate result

Disadvantages: time consuming

Expensive

Large volume of data to process

Random sampling

a method of selecting a group ( sample) from a larger population in such a way that every member of the population has an equal chance of being chosen