CH 2.1 frequency distribution for organizing and summarizing data

frequency distribution

also known as a frequency table, it is helpful in organizing and summarizing data.

lower class limit

the smallest numbers that can belong to each of the different classes

upper class limits

the largest numbers that can belong to each of the different classes

class boundaries

the numbers used to separate the classes, but without the gaps created by class limits

class midpoints

the values in the middle of the classes. Add the lower class limit to the upper class limit and divide by 2

class width

the difference between two consecutive lower class limits in a frequency distribution

relative frequency

Each class frequency is replaced by a relative frequency or a percentage

cumulative frequency distribution

the frequency for each class is the sum of the frequency for that class and all previous classes

normal distribution

-the frequencies start low, then increase to one or two high frequencies, and then decrease to a low frequency

-the distribution is approximately symmetric

gaps

the presence of gaps can show that the data are from two or more different populations. however, the converse is not true, because data from different populations do not necessarily result in gaps.