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**Population and Sampling**

- Population – all individuals / items of interest.
- Census – observation or measurement of every member of population.
- Sample – selection of individuals from population taken to find out more information about entire population.
- Sampling Units – individual units of population.
- Sampling Frame – list of sampling units in form of names / numbers.

When it comes to AS/A-level Maths, can you differentiate systematic sampling and stratified sampling?

**Random Sampling**

- Every member of population has equal chance of selection.
- Representative sample.
- All require sampling frame.

(1)**Simple**– every sampling unit has equal chance of selection.

(2)**Systematic**– required number of sampling units taken at regular intervals from a sampling frame.

(3)**Stratified**– population divided into mutually exclusive strata and then simple random sample taken from each.

**Non-random Sampling**

- Quota: interviewer selects representative sample reflecting characteristics of whole population.
- Opportunity: taking sample from available subjects who fit criteria at time.

**Types of Data**

- Quantitative: numerical observation e.g. shoe size.
- Qualitative: non-numerical observation e.g. hair colour.
- Continuous: can take any value in given range e.g. time.
- Discrete: can only take specific values in given range e.g. number of students in a year.

**Grouped Data**

- Large amounts of data displayed in frequency table.
- Classes - there are no specific values.
- Class boundaries - tell you max and min value in each class.
- Midpoint - average of class boundaries.
- Class width - difference between upper and lower class boundaries.

**Large Data Set Variables**

- Daily mean temperature - measured hourly.
- Daily total rainfall - including ice / snow that melts.

- Amounts less than 0.5mm recorded as ‘tr’ for trace. - Daily total sunshine - recorded to nearest tenth of hour.
- Daily mean wind direction and speed - averaged over 24 hours.

- Directions = bearings

- Speed = Beaufort Scale - Daily maximum gust - direction and highest wind speed recorded in knots.
- Daily maximum relative humidity - above 95% means foggy, misty conditions.
- Daily mean cloud cover - measured in oktas.
- Daily mean visibility - decametres greatest horizontal distance which object can be seen.
- Daily mean temperature - HPa, Hectopascals.

That's the end of the topic!

Drafted by Bonnie (Mathematics)