Statistics equations

Question 1

What is a population?

Answer 1

The whole set of items that are within interest (eg. group of people, apples in a basket)

Question 2

What is a census?

Answer 2

An observation of every member within a population

Question 3

What is a sample?

Answer 3

A selected subsection of members from a population (in order to gather info about the whole population)

Question 4

What is a sampling frame?

Answer 4

A list of individually written/ numbered sampling units

Question 5

What are the advantages of a sample compared to a census?

Answer 5

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)

Question 6

What is a simple random sample?

Answer 6

A sample where every member has an equal chance of being selected

Question 7

What is systematic sampling?

Answer 7

Where samples are taken at regular intervals from an ordered list

Question 8

What is stratified sampling?

Answer 8

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)

Question 9

What is random sampling?

Answer 9

When a sample of the population is chosen at random to remove any bias

Question 10

What is quota sampling?

Answer 10

When a sample is taken of members that reflect on the whole population

Question 11

What is opportunity (convenience) sampling?

Answer 11

When a sample is taken from members of a population that are available at the time who fit the criteria

Question 12

Compare random to non-random sampling

Answer 12

Random sampling allows for the bias to be removed, whereas non-random sampling produces a bias that wont represent the population accurately

Question 13

What are the types of data and state what each one consists of

Answer 13

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)

Question 14

What is the class width?

Answer 14

The difference between the lower and upper class boundaries

Question 15

What are all the mean variables you can get on a large data set?

Answer 15

Temperature / wind direction and wind speed (with Beaufort scale)/ cloud coverage / visibility / pressure

Question 16

What are the total variables you can get on a large data set?

Answer 16

Rainfall / sunshine

Question 17

What are the maximum variables you can get on a large data set?

Answer 17

Gust / relative humidity

Question 18

How do you work out the mean?

Answer 18

Add all values together then divide by how many values there are (eg. 5+7+2+1+4+5/ 6 = 4)

Question 19

How do you work out the median value?

Answer 19

Median value is the middle value of an ordered list of values

Question 20

What is the mode?

Answer 20

The variable value with the highest occurring value frequency

Question 21

How do you find the lower and upper quartile?

Answer 21

Lower: n/4
Upper: 3n/4

Question 22

What does Q1, Q2 and Q3 stand for

Answer 22

Q1 - lower quartile
Q2 - median
Q3 - upper quartile

Question 23

How can you work out a percentile value?

Answer 23

The same way as you do to find a quartile value, by interpolation

Question 24

How to you work out the IQR (inter quartile range)?

Answer 24

Upper quartile - lower quartile

Question 25

What is the link between the variance and standard deviation?

Answer 25

Standard deviation is the square root of the variance

Question 26

How can you calculate estimates for the standard deviation and variance of data on a frequency table?

Answer 26

By using the midpoint of each interval and multiplying it by the frequency to get the values to use for x in the equations

Question 27

Why do we code data?

Answer 27

To create smaller or larger values that are more manageable to work with