Statistics

Question 1

What is random sampling?

Answer 1

Usually using computer generated random number tables. Every item has an equal chance of being selected

Question 2

What is stratified sampling?

Answer 2

The area under study is divided up into homogenous units and each unit is randomly or systematically sampled

Question 3

What is systematic sampling?

Answer 3

Items are picked at a regular interval e.g. every 30 metre

Question 4

Outline a bar graph:

Answer 4

Easy to understand

Histograms are bars based on frequencies

Question 5

Outline a line graph:

Answer 5

Used for continuous data
Can plot several lines on one graph
Can have different scales on each axis

Question 6

Outline a pie chart:

Answer 6

The segments represent the share of the total value

Visual but can be difficult to read

Question 7

How do you work out the mean?

Answer 7

Calculated by adding up all the values in a datset and dividing the total sum by the number of values in the data set.

Question 8

What is the median?

Answer 8

This refers to the central value in the ranked data set.

Question 9

What is the mode?

Answer 9

This is the most frequently occurring number in the data set.

Question 10

What is the range?

Answer 10

Highest value take away the lowest value.

Question 11

What happens when the median, mode and mean are the same value?

Answer 11

We get a normal distribution, however, most data sets are SKEWED with differences in the 3 measures.

Question 12

Outline how to work out interquartile range:

Answer 12

1) Put numbers in order.
2) Find out the median
3) Find the median of the data set before and after the median number (upper and low quartile)
4) Take upper away from lower quartile to get the interquartile range.

Question 13

What is standard deviation?

Answer 13

The standard deviation is the most useful measure of the dispersion of a set of data from its mean.

A low SD indicates that the data is clustered around the mean whereas a high value indicates dispersion.

Question 14

Outline how to calculate standard deviation:

Answer 14

1) Difference of each value from the mean is worked out.
2) Each of these values is squared (to remove negative values)
3) All the squared values are added together
4) This summed value is then divided by the number of values in the data set.
5) The square root of this value is found.

Question 15

What is the formula for standard deviation?

Answer 15

SD = ∑ ( x - x )²
_______
n

n = number of values in the data set 
x = each value in data set
Second x (should have a line over)  = mean of all values in data set

Question 16

What are the advantages of using standard deviation?

Answer 16

Shows how much data is clustered around a mean value

It gives a better idea of how the data is distributed

Question 17

What are the disadvantages of using standard deviation?

Answer 17

It doesn’t give you the full range of the data

It can be hard to calculate

Only be used with data which can be plotted on a histogram so where a independent variable is plotted against frequency of it.

Question 18

What is the formula for Spearman’s rank?

Answer 18

Rs = 1 - 6 ∑ d²
_______
n3 - n

n = rank 
d= difference

Question 19

What does the result mean from spearman’s rank?

Answer 19

If value is greater than 0.05 level of significance value - 95% confident that there is a relationship between the two variables

• Over 0.01 = 99% confidence
• if value is below critical value, null hypothesis is accepted.

Question 20

What is GIS?

Answer 20

Geographical Information Systems

The use of computer software to link a variety of data to a location.

Question 21

What are the uses of GIS?

Answer 21

Might be that a company needs information on socio-economic groupings within a town in order to decide where best to locate their new store.

The GIS database for that application might also have data on the location of similar stores, the transport infrastructure & council tax rates.

Question 22

What are the advantages of using GIS?

Answer 22

It allows information to be presented in a visual and easily understood format.

Different types of information can be overlain onto base maps of an area.

Question 23

Advantages of using a bar chart?

Answer 23

• show relationships between 2 or more variables
• visually attractive
• Can show positive and negative values
• Simple to construct and read

Question 24

Advantages of using pie charts?

Answer 24

• visually attractive
• shows proportion of components
• shows scale

Question 25

Weaknesses of using bar graphs?

Answer 25

• Plotting too many bars makes it appear cluttered- less easy to interpret
• Using too many or too few classes can mask important patterns in the data

Question 26

Weaknesses of using pie charts?

Answer 26

• Less than 3 segments look simplistic

- If many segments a similar size; it is hard to interpret