Chapter 3 Flashcards
Enumeration
Listing all points in a data set.
Tabular frequency distribution
A table that lists the numerical values of a variable in a logical order along with frequency of each value.
Frequency
Usually abbreviated âfâ is the number of times a particular value of the variable occurs.
How does a tabular frequency distribution show the values of a variable?
In order with largest value first.
What is another name for a grouped frequency distribution?
Frequency distribution using class intervals.
Grouped frequency distribution
A frequency distribution with adjacent values of the variable grouped together. The use of class intervals generally makes a frequency distribution easier to understand. Class intervals must be of the same width and it is generally desirable to have between 6 and 20 intervals.
What are the six steps for creating a grouped frequency distribution?
- Find the range of scores (highest score minus lowest score).
- Make a preliminary choice of the desired number of class intervals.
- Determine the interval width by dividing the range of by the number of class intervals. Round the interval width in either direction to an even number.
- Determine the lower limit of the lowest interval.
- Prepare a list of the limits of each class interval, beginning at the bottom of the table with the lowest score and proceeding upward.
- Count the number of observations that occur in each interval and enter that count as the frequency of the interval.
Histogram
A graphical presentation of a grouped frequency distribution with frequencies represented as vertical bars (next to each other); it is appropriate for interval/ratio data.
Frequency polygon
A graphical presentation of a grouped frequency distribution with frequencies represented as points ; it is appropriate for interval/ratio data.
Relative frequency
Frequency divided by the size of the group, expressed as a proportion or percentage.
Stem and leaf display
Optional way of presenting frequency distributions of interval/ratio data - not as widely used.
What are the five steps for eyeball estimating a frequency distribution?
- Axes - Draw and label the axes. X axis has the variable you are interested in. Vertical axis has the frequency (f).
- Min and Max - Plot your estimates to the minimum and maximum of the variable.
- Intermediate - Add intermediate values to the X-asis using round numbers.
- Mode - Plot estimate(s) of the mode(s) of the frequency distribution.
- Complete - Connect the parts of the sketch that you have just created, keeping the distribution smooth and continuous.
Where is the mode on a frequency distribution?
The mode is the most frequently occurring value in a distribution; it lies directly below the highest point on a graphical frequency distribution.
Unimodal distribution
A distribution that has one most frequently occurring value.
Bimodal distribution
A distribution that has two most frequently occurring values.
Symmetric distribution
A distribution whose left side is a mirror image of its right side.
What type of distribution is usually found in nature?
Unimodal. Bimodal distributions only occur when there is a splitting of a population into relatively distinct parts.
Positively skewed distribution
A distribution whose right tail is longer than its left tail.
Negatively skewed distribution
A distribution whose left tail is longer than its right tail.
Asymptotic
A distribution whose tail gradually approaches the x-axis but never actually touches it.
Normal distribution
Normal distributions are unimodal, symmetric, and asymptotic which means they have a general bell shape.
Bar graph
A graphical display of a frequency distribution where frequencies are represented as separated vertical bars. Used for nominal or ordinal data.
What does the separation of the bars in a bar graph indicate?
Makes it clear that there are no intermediate values were measured and also that the order of the bars can be rearranged.
How are the frequency distributions of ordinal data displayed?
Bar graphs, histograms or frequency polygons.
What is the advantage using a bar graph for ordinal data?
It makes it clear that the intervals between points are not necessarily equal sized
What is the disadvantage using a bar graph for ordinal data?
It implies that there are no intermediate values between the bars.
What graphs should be be used for interval/ratio level data?
Histograms or frequency polygons.
What graphs should be be used for nominal data?
Bar graphs.
What graphs should be be used for ordinal data?
Bar graphs.
