FREQUENCY DISTRIBUTION Flashcards
is a graphical technique that
organizes data into a histogram-like display.
STEM PLOTS
It is an excellent way to begin an analysis and is a good way to learn several important statistical principles.
steam-and-leaf plot (stem plot)
components of setm and leaf plot
Stem
Leaf
Three aspects of the distribution are
now visible:
Shape
Location
Spread
refers to the configuration of data points as they
appear on the graph.
Shape
This is seen as a ’skyline silhouette’.
Shape
A distribution’s shape can be discussed in terms
of its
Symmetry
modality
kurtosis
refers to the degree to which the
shape reflects a mirror image of itself around
it center.
Symmetry
is a measurement of the
distortion of symmetrical distribution or
asymmetry in a data set.
Skewness
refers to the number of
peaks on the distribution.
Modality
3 kinds of modality
unimodal
bimodal
multimodal
refers to the steepness of the mound.
Kurtosis
3 kinds of kurtosis
mesokutric curve
leptokurtic curve
platykurtic curve
Distributions that are moderate in breadth and curves with a medium peaked height.
Mesokurtic:
More values in the distribution tails and more values close to the mean (i.e. sharply peaked
with heavy tails)
Leptokurtic:
Fewer values in the tails and fewer values close to the mean
Platykurtic:
the curve has a flat peak and
has more dispersed scores with lighter tails
Platykurtic:
sharply peaked
with heavy tails
Leptokurtic
refers to the center of a
distribution.
average
two different ways to identify a
distribution’s average
arithmetic average
median
is a distribution’s
gravitational center.
arithmetic average
is the point that divides the
data set into a top half and bottom half
median
has a depth of (n +1)/ 2
median
is the sample size
n
When n is
even, the median will fall between
2 values
is an informal way to refer to the dispersion or
variability of data points
Spread
3 Measures of Variation
Range (highest - lowest)
Standard Deviation
Variance
tables are a traditional way to describe the distribution of counts in a data set.
Frequency
Three types of frequencies
frequency column
relative frequency
cumulative frequency
column that contains counts
frequency
column contains frequency counts
divided by the total with values expressed as a percentage
relative frequency
column contains precents that fall
within or below a given level
cumulative frequency
is one which can take only isolated values
discrete variable
Normally, it does not carry any fractional
value. Usually it is the result of counting something
discrete variable
is also called a discontinuous variable
discrete variable
is capable of assuming any fractional value within a specified range of values.
continuous variable
It is the result of measuring something.
continuous variable
2 Class-limits
lower limit
upper limit
the smallest possible measurement in a class is known as lower limit
lower limit
the highest possible measurement
upper limit
is the point
lying halfway between the lower limit and the upper limit.
Mid-point of a Class Interval
mid point formula
(L + U) / 2
meaning of L in midpoint formula
lower limit
*
meaning of U in midpoint formula
upper limit
means the difference between the upper
limit and lower limit of a class interval.
magnitude of a class interval
Two types of classification according to the class-intervals
exclusive method
inclusive method
in this method the upper limit of a class becomes the lower limit of the next class.
exclusive method
in this method we do not put any item that is equal to the upper limit of a class in the same class but we put it in the next class
exclusive method
here, the upper limits of classes are excluded from them
exclusive method
in this method the upper limimt of any class interval is kept in the same class-interval
Inclusive method
in this method the upper limit of a previous class is less by 1 from the lower limit of the next class interval.
inclusive method
this method allows a class-interval to include both its lower and upper limits within it
inclusive method
4 kinds of frequency charts
Bar charts
Histograms
Frequency Polygon
Pie charts
is a good choice when you want to compare the frequencies of different values.
It’s much easier to compare the heights of bars than the angles of pie chart slices.
bar chart
2 types of bar graphs
horizontal bar graphs and vertical bar graphs
horizontal bar graphs and vertical bar graphs
bar graphs
the bars are placed continuously side by side without a gap between consecutive bars.
Histograms
is a line graph of class frequency plotted against class midpoint
frequency polygon
It can be obtained by joining the midpoints of the tops of the rectangles in the histogram
frequency polygon
is a circle that’s divided into one slice for each value.
pie chart
in pie charts, the size
of the slices shows their —-
relative frequency
