Everything you need to know! Flashcards
What information goes along the horizontal axis of a population pyramid?
Percentage (of the total population)
What are the key features of a stem and leaf diagram?
Key
Numbers in the leaves in order and in line with each other
Stem on the left hand side (or down the middle if it’s a double sided stem and leaf diagram)
How do calculate the mean?
Add up the data items and divide by how many there are
Name three ways in which charts can be misleading.
No scales on their axes
A false origin (the vertical scale doesn’t begin at zero)
Bars not drawn in proportion (i.e. different widths)
Missing axes
What does x with a line over the top (x bar) stand for?
This is the mean of the data set. We use it when finding the standard deviation
How do you find the range of data displayed in a stem and leaf diagram?
Find the smallest number. Find the largest number in the diagram. Work out the difference.
How do you find the mode of data displayed in a stem and leaf diagram?
Find which number occurs most often. Be careful: don’t just look in the leaf. You need to write down the full number i.e. 3 l 7 is 37 not 7
How do you find the median of data displayed in a stem and leaf diagram?
Cross off the smallest and the largest number. Then the next smallest and the next largest number. Keep going until:
a) you have one number left - the median
b) you have two numbers left - the median is the middle of these two numbers
How do you find the mean of data displayed in a stem and leaf diagram?
Just like data in a list, you need to add up the data items and divide by how many there are
When is the mean not a suitable average?
When one number is a long way from the others - because this mean involves adding all numbers up, this situation would make the mean much lower/higher than it should be
Why is this statement misleading?
Sales increased £3 million over the last year
We’re not told what they increased from. £3 million might be a huge increase for a small company or a small increase for a company as big as Tesco
What is primary data?
Data which you collect yourself
What is secondary data?
Data which is collected from published statistics or databases
What are the advantages of primary data?
You know how the data was collected
You know who the data was collected from
What are the disadvantages of primary data?
Time consuming
Expensive
Describe how to take a simple random sample
Assign each member of the population a unique numberUse a random number generator to generate random numbers until the sample is filledIgnore any repeated values
What is raw data?
Raw data is data which has not been ordered or processed in any way.
What are the advantages of secondary data?
Cheap
Easy to obtain
What are the disadvantages of secondary data?
May be out of date
You don’t know how or who it was collect from
What does it mean for a sample to be biased?
It is not representative of the population
What is the key feature of a stratified sample?
The groups in the sample are in the same proportion as they are in the population.For example, if have the population is male, half the sample should also be male.
What is convenience sampling? Why is it a problem?
The most convenient sample is chosen. For example, if you want to sample ten people, you sample the first ten people you meet. This will likely give a biased sample as the choice of the sample is at the discretion of the surveyor
What is the difference between quantitative and qualitative data?
Quantitative - numerical data i.e. price, length Qualitative - non-numerical data i.e. car brand, eye colour
Quantitative (numerical) data can be split into two different groups - what are these?
Discrete
Continuous
What is the difference between discrete and continuous data?
Continuous data can take any value within a range. Discrete data can only take particular values.
What is it called when we sample every member of a population?
A census
What are the key points to remember when drawing a frequency polygon?
Plot the points above the midpointsPlot frequency up the vertical axisJoin each point to the next one with a straight line
What are the key points to remember when drawing a cumulative frequency curve?
Plot the points above the upper class boundaryPlot cumulative frequency on the vertical axisJoin the points with a smooth curve
What are the advantages of using a sample over a census?
Cheaper
Less time-consuming
Reduces the amount of data to be collected and analysed
What are the disadvantages of using a sample over a census?
May be biased
Not totally representative
What are the advantages of using a census over a sample?
Accurate
Unbiased
Every member of the population is represented
What are the disadvantages of using a census over a sample?
Expensive
Time-consuming
Difficult to ensure the whole population is surveyed
A Spearman’s Rank Correlation Coefficient of +1 means what?
Perfect agreement between the two rankings
A Spearman’s Rank Correlation Coefficient of -1 means what?
Perfect disagreement between the two rankings
A Spearman’s Rank Correlation Coefficient of 0 means what?
The rankings neither agree nor disagree
What is the difference between an explanatory and a response variable?
In an experiment, the variable which is being controlled is called the explanatory (independent) variable. The effect observed is called the response (dependent) variable
What is bivariate data?
Data for two different (usually related) variables – for example, ice cream sales and temperature
What do I need to remember when drawing a line of best fit?
Use a ruler
The line must go through the mean point (x ̅,y ̅ ) – this is the mean of the x values plotted against the mean of the y values
Draw the line so that you have the same points above and below it, or as close to this as possible
