Statistics gcse

Things to consider when collecting data

• The sample size

• whether it’s representative

• Whether it’s biased

How to avoid bias

Sampling method or by increasing the sample size

How to collect data

Questionnaires

Interviews

Observations

Surveys

Mean

Total number of all values divided by the number of values

Median

The middle value

Mode

The most common value

Range

The difference between the highest and lowest value

Interquartile range

Upper quartile - lower quartile

Ways to represent quantitive data

Table, bar chart, scatter graph etc

Representing qualitative data

Use a pie chart etc

Examples of bias in surveys

Voluntary response sampling- People have chosen to take the survey

Response bias - The wording makes people not want to answer truthfully

Convenience sampling - the first people to show up

Non response - people don’t reply so their pov is missed

Non random sampling

Voluntary: asking people to do a survey

Convince: Sampling the first people to show up

Pros of grouped data

• Makes the data easier to read and understand

• Easier to spot patterns and compare data

Cons of grouped data

• Lose accuracy of the data as you no longer know the exact values

• Calculations made from these will only be an estimate

Laboratory experiments

• Researcher has full control of the variables

• Easy to replicate

• People may react differently to normal under test conditions

Field experiments

• Carried out in an everyday environment

• Researcher has some control of the variables

• Not easy to replicate and it’s hard to control extraneous variables

Natural experiments

• Carried out in the everyday environment

• Researcher has no/little control of the variable

• Reflects real life behaviour

• Low validity due to little control of the variables and it’s difficult to replicate

Frequency density equation

Frequency density = Frequency/ class width

Types of misleading diagrams

• Pictograms - same symbol and size need to be used for all the diagrams and a key is needed

• 3d charts - Distort part of the diagram making it difficult to read the values

• Colours - Some colours make part of the diagram stand out more, making it seem more important

• Lines drawn too thick make it difficult to read information

Axes and scales that can be misleading

• A scale that does not start at zero

• Missing values on the scales

• Axes that are unevenly scales

• Axes that are not labelled

• Not using a key

Bivariate

Involves measuring two variables

Multivariate

Made up of two or more variables

eg: comparing height, weight, age and shoe size together

cluster sampling

The population is put into random groups, one group is randomly selected and everyone in the group is asked

Census

Collects information from all members of a population

Lower class boundary

The smallest number in the class

Pilot study

A pilot study is a small scale study that is conducted to inform, predict and direct an intended future scale study

Opinion scale

An opinion scale lets people express their feelings on a numbered scale

How to calculate an index number

Current price divided by base year price then x100