GCSE Statistics Revision

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GCSE Statistics Revision

• Block 1Basic Ideas and Vocabulary

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Introduction

• Population
• All the people or objects being studied
• Sample
• A representative selection from the population
• Data
• Information collected from the sample
• Hypothesis
• An idea about the population using the sample as
  evidence

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Data

• Primary or Secondary
• Original or second hand data
• Qualitative or Quantitative
• Descriptive or numerical data
• Discrete or Continuous
• Taking fixed values or any value in the range
• Class Boundaries
• Making sure that there are no gaps and no
  overlaps in the interval ranges

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Organising Data

• Categorical Data
• Data is organised by category eg Insurance Group
  of cars
• Ranked Data
• Data is sorted into order 1st, 2nd 3rd etc
• Interval Data
• One value represents all values in that range
• Ratio Data
• On a multiplicative not additive scale

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Organising Data (2)

• Bivariate Data
• Data which occur in pairs eg (Height, Weight)
• Grouped / Ungrouped Data
• Be careful not to lose accuracy!
• 2-Way Tables
• Sort the data according to two characteristics
• Explanatory Response Variables
• Independent and Dependent variables

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Sampling

• Census
• Sample Population
• Sampling Frame
• Every member of the population able to be
  included in the sample
• Representative
• The sample perfectly reflects the population
• Unbiased
• The sample is fair and balanced

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Randomness

• Random
• Equivalent to pure chance
• Ran on Calculator
• 500xRan gives random numbers 0 to 500
• Random Number Tables
• Create sets of random numbers of any size
• Simulations
• Use dice, coins, ICT, RNT etc to model chance

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Stratified Sampling

• Divide the population into Strata
• Use a Two-Way Table to sort the data
• Decide the sample size required
• Write this as a fraction of the whole population
• Take this fraction from each stratum to create
  your sample
• This is usually the best sampling technique

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Other Sampling Techniques

• Systematic Sampling
• e.g. Take the first 20 or every 7th one
• Quota Sampling
• Choose respondents according to preset criteria
• Cluster Sampling
• Split population into many small groups the
  sample consists of several of these groups
• Convenience Sampling
• Grab what you can! (Emergency use only)

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Questionnaires

• The INTERVIEWER asks the RESPONDENT
• Open Questions
• Free to answer at length
• Closed Questions
• Multiple Choice option boxes
• Ideal Questions
• Short
• Simple, clear language
• No ambiguity or bias
• Pilot Survey

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Other Ideas

• Accuracy
• Half a unit either side
• e.g. 2.7m means 2.65m to 2.75m
• Upper and Lower bounds
• Good design
• Minimising bias and ambiguity
• Anticipating problems
• Sample represents population