Statistics equations Flashcards
What is a population?
The whole set of items that are within interest (eg. group of people, apples in a basket)
What is a census?
An observation of every member within a population
What is a sample?
A selected subsection of members from a population (in order to gather info about the whole population)
What is a sampling frame?
A list of individually written/ numbered sampling units
What are the advantages of a sample compared to a census?
A sample is much more efficient and less time consuming than a census, however it may not be as accurate. (A census may also destroy all items in a population which would lead to no items being left to be sold)
What is a simple random sample?
A sample where every member has an equal chance of being selected
What is systematic sampling?
Where samples are taken at regular intervals from an ordered list
What is stratified sampling?
Where a population is divided into mutually exclusive strata (groups of similarity, eg female group and male group) then a random sample is taken from each stratum (from each group)
What is random sampling?
When a sample of the population is chosen at random to remove any bias
What is quota sampling?
When a sample is taken of members that reflect on the whole population
What is opportunity (convenience) sampling?
When a sample is taken from members of a population that are available at the time who fit the criteria
Compare random to non-random sampling
Random sampling allows for the bias to be removed, whereas non-random sampling produces a bias that wont represent the population accurately
What are the types of data and state what each one consists of
Numerical - quantitative (numbers)
Non-numerical - qualitative (adjectives such as colours/ names)
Continuous - any values within a range (time can be 2s or 3.75s / decimal values)
Discrete - specific values within a range (5 girls or 7 boys / exact values)
What is the class width?
The difference between the lower and upper class boundaries
What are all the mean variables you can get on a large data set?
Temperature / wind direction and wind speed (with Beaufort scale)/ cloud coverage / visibility / pressure
What are the total variables you can get on a large data set?
Rainfall / sunshine
What are the maximum variables you can get on a large data set?
Gust / relative humidity
How do you work out the mean?
Add all values together then divide by how many values there are (eg. 5+7+2+1+4+5/ 6 = 4)
How do you work out the median value?
Median value is the middle value of an ordered list of values
What is the mode?
The variable value with the highest occurring value frequency
How do you find the lower and upper quartile?
Lower: n/4
Upper: 3n/4
What does Q1, Q2 and Q3 stand for
Q1 - lower quartile
Q2 - median
Q3 - upper quartile
How can you work out a percentile value?
The same way as you do to find a quartile value, by interpolation
How to you work out the IQR (inter quartile range)?
Upper quartile - lower quartile
What is the link between the variance and standard deviation?
Standard deviation is the square root of the variance
How can you calculate estimates for the standard deviation and variance of data on a frequency table?
By using the midpoint of each interval and multiplying it by the frequency to get the values to use for x in the equations
Why do we code data?
To create smaller or larger values that are more manageable to work with
