Statistics Mind Map

The mean of grouped data is the average value found by using class marks and frequencies of the grouped table.

Always write the class mark first, then multiply by frequency, and keep the total frequency in the denominator.

The assumed mean method is a shortcut for finding the mean of grouped data by taking one convenient central value as a reference.

Choose a class mark near the center of the data to keep deviations small and calculations simple.

The step deviation method is a fast way to find the mean of grouped data when class widths are equal.

Check the class width first. If all intervals are equal, step deviation can save time in the board exam.

The median of grouped data is the middle value that divides the frequency distribution into two equal parts.

Always find N/2 first and then locate the class where the cumulative frequency first becomes greater than or equal to N/2.

The modal class is the class interval with the highest frequency in grouped data.

Before using the mode formula, mark the class that has the highest frequency; that is the modal class.

The mode of grouped data is the value that occurs most frequently, estimated using the modal class and a standard formula.

Always identify the modal class first, then use the three frequencies around it carefully in the formula.

Cumulative frequency is the running total of frequencies up to a class interval.

Check the running total after every row; one wrong addition can affect the full table and the median.

A less-than cumulative frequency table lists the number of observations less than each upper class boundary.

Write the upper class boundary carefully; the graph and median position depend on it.

An ogive is a cumulative frequency graph used to interpret grouped data and locate values such as the median.

For an ogive, always plot cumulative frequency against class boundary, not class mark.

The median from an ogive is found by using the total frequency, locating N/2 on the cumulative frequency axis, and reading the corresponding class boundary value.

Use a ruler and mark the horizontal and vertical steps carefully; one small reading error changes the answer.

The class mark is the midpoint of a class interval and is used as the representative value of that class in grouped-data calculations.

If the class interval is written as a range, the midpoint is almost always the safest representative value.

Comparing central tendency measures means deciding whether mean, median, or mode best describes a data set for a given situation.

Read the situation first: balanced data often suits mean, skewed data often suits median, and most common item questions often suit mode.