# 2. Data Presentation and Interpretation

Flashcards by Riya Patel, updated more than 1 year ago
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Edexcel Mathematics A Level Paper 2: Statistics and Mechanics
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 Question Answer Define 'measure of location' A single value which describes a position in a data set Define 'measure of central tendency' A single value that describes the centre of the data When is it suitable to use the mode? When data is qualitative, or quantitative with either a single mode or two modes (bimodal) When is it suitable to use median? For quantitative data and usually when there are extreme values as median is not affected by them When is it suitable to use the mean? For quantitative data and as it uses all pieces of data, it gives a true measure of the data but is affected by extreme values What is the formula used for calculating the mean of data given in a frequency table? ∑xf is the sum of the products of the data values and their frequencies ∑f is the sum of the frequencies Frequency Table Mean (binary/octet-stream) What do percentiles do to a data set? Split it into 100 parts What is the formula used to find the lower quartile? (n+1) / 4 What is the formula used to find the median? (n+1) / 2 What is the formula used to find the upper quartile? 3(n+1) / 4 Name the technique used to estimate the median, quartiles and percentiles when data is presented in grouped frequency tables Interpolation What assumption is made when using interpolation? That the data values are evenly distributed within each class What is the formula used for interpolation? Interpolation (binary/octet-stream) Define 'variance' How much each data point deviates from the mean by a certain amount What is Sxx and what is it's formula? It is the sum of the squares Sxx (binary/octet-stream) What is the formula for variance? Variance (binary/octet-stream) What are the units of variance? The units of the data squared What is the formula for standard deviation? It is the square root of the variance Standard Deviation (binary/octet-stream) What are the formulae for standard deviation and variance for grouped data that is presented in a frequency table? Frequency Sd And Variance (binary/octet-stream) Define 'coding' It is a way of simplifying statistical calculations and involves each data value being coded to make a new set of data values which are easier to work with What is the formula typically used to code data? Where a and b are constants you have chosen or are given Coding (binary/octet-stream) If data is coded using the formula y=(x-a)/b, what is the mean of the coded data given by? Coding Mean (binary/octet-stream) What is the standard deviation of the coded data given by? Coding Sd (binary/octet-stream) Define 'outlier' An extreme value that lies outside the overall pattern of the data Commonly defined as any value that is either greater than Q3 + k(Q3-Q1) or less than Q1 - k(Q3-Q1) Define 'anomalies' These are outliers that should be removed from the data set since it is clear that is an error What is the process of removing anomalies from data known as? Data cleaning What makes a data value an outlier? If it is significantly higher or lower than the mean + standard deviation Name the diagram you can use to estimate the values of the median, quartiles and percentiles if you are given data in a grouped frequency table Cumulative frequency diagram What type of data can be represented in a histogram? Grouped continuous data In a histogram, what is the area of a bar proportional to? The frequency in each class In a histogram, what does the height of each bar represent? Frequency density What is the formula for frequency density? Freq Density (binary/octet-stream) What does joining the middle of the top of each bar in a histogram form? A frequency polygon When comparing data sets, what are the two things you can comment on? A measure of location (median, mean, mode) A measure of spread (quartiles, variance, SD) Define 'bivariate data' Data which has pairs of values for two variables (represented on scatter diagrams) Comment on the correlation Strong Ve (binary/octet-stream) Strong negative correlation Comment on the correlation Weak Ve (binary/octet-stream) Weak negative correlation Comment on the correlation No Correlation (binary/octet-stream) No (zero) linear correlation Comment on the correlation Weak +Ve (binary/octet-stream) Weak positive correlation Comment on the correlation Strong +Ve (binary/octet-stream) Strong positive correlation What is a least squares regression line? The straight line that minimises the sum of the squares of the distances of each data point from the line What are regression lines used for and what is this called? To make predictions for values of the dependent variable that are within the range of the given data Interpolation What is the name of the method used to make predictions based on a value outside the range of the given data? Extrapolation What is the main issue associated with using extrapolation to predict values? It gives a much less reliable estimate

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