Data presentation
Practice Flashcards
What does a frequency table show?
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All Flashcards in Topic 4.2
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4.2.19 cards
What does a frequency table show?
Each data value (or class) together with its frequency — how many times it occurs.
What is the mode?
The data value that occurs most often (the highest frequency).
How do you find the total number of data values from a frequency table?
Add up all the frequencies.
What is a histogram?
A display of grouped continuous data using touching bars.
On a histogram with equal-width classes, what does the bar height show?
The frequency of that class.
Why do histogram bars touch?
The data is continuous, so the classes are adjacent intervals with no gaps.
What is the modal class?
The class (interval) with the greatest frequency — the tallest bar.
Difference between a histogram and a bar chart?
Histograms show continuous data (bars touch); bar charts show categories (bars have gaps).
Mode vs frequency — what's the trap?
The mode is the data value itself, not the frequency written beside it.
4.2.29 cards
What is cumulative frequency?
A running total of the frequencies up to the top of each class.
Where do you plot a cumulative frequency value?
At the upper boundary of its class.
What shape is a cumulative frequency graph?
A smooth increasing S-shaped curve (an ogive).
How do you read the median from the curve (n values)?
Read across from a cumulative frequency of n/2, down to the data axis.
How do you read the lower and upper quartiles?
Read across from n/4 (Q1) and 3n/4 (Q3).
How do you find the IQR from the curve?
IQR = Q3 − Q1.
How do you find how many values lie between a and b?
Subtract the cumulative frequency at a from the cumulative frequency at b.
What is the 90th percentile?
The value below which 90% of the data lie — read across from 0.9n.
How do you find the value the top X% exceed?
Read across from (100 − X)% of n, since the curve counts values below a level.
4.2.39 cards
What five numbers does a box plot show?
Minimum, lower quartile Q1, median, upper quartile Q3, maximum.
What does the box span?
From Q1 to Q3 (the middle 50% of the data), with the median marked inside.
What is the range?
Maximum − minimum.
What is the interquartile range (IQR)?
Q3 − Q1 — the spread of the middle 50%.
What fraction of the data is in each box-plot section?
About 25% (a quarter) in each of the four sections.
State the outlier rule.
A value is an outlier if it is below Q1 − 1.5·IQR or above Q3 + 1.5·IQR.
How do you test whether a value is an outlier?
Find IQR, then the fences Q1 − 1.5·IQR and Q3 + 1.5·IQR; compare the value with them.
How do you compare two distributions from box plots?
Compare the medians (centre) and the IQRs or ranges (spread).
Range vs IQR — what's the difference?
Range uses the extremes (max − min); IQR uses the quartiles (Q3 − Q1), so it ignores outliers.
Topic 4.2 study notes
Full notes & explanations for Data presentation
Math AA SL exam skills
Paper structures, command terms & tips
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