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Descriptive statistics sumerize or describe the important chaacteristics of a set of data.
Inferential statistics use inferences that go beyond the known data.
MEASURE OF CENTER
A measure of center is a value at the center or middle of a data set.
The arithmetic mean
of a set of values is the measure of center found by adding the values and dividing the total by the number of values. It is what most people call the average. Can be effected by an extreme value.
- Mean = (SIGMA) (greek weird E thing)X/n
- This symbol means the other values need to be added Ex represents the sum of all data values. n = the number of sample values
- greek mu ( u) if all values of a population are used
- x with a line over it xbar used to denote mean if the data is a sample set
- simple statistics are english letters parameters use greek letters.
The median of a data set is the measure of center that is the middle value when the original data values are arranged in order of increasing or decreasing magnitude. The median is often denoted a by x with a squiggle line over it x-tilde. Like a spanish x
TO FIND THE MEDIAN
sort the values in order. If the number of values is odd the median is the middle number. If thr number of values is even the median is found by computing the mean of the middle numbers.
- X~ = 5.40 1.10 0.42 0.73 0.48 1.10 SORT 0.42 0.48 0.73 1.10 1.10 5.40
- then 0.73 + 1.10/ 2 ( the number of values) = 1.83/2=0.915
The mode is the set of data that occurs most frequently.
When 2 values occur with the same greatest frequency, each one is a mode and the data set is bimodal.
When more than 2 values occur with the same greatest frequency, each is a mode and the data set is considered to be multimodal.
When no value is repeated, we say there is no mode.
- The midrange is the measure of center that is the value midway between the maximum and the minimum values in the original data set. It is found by adding the maximum data value to the minimum data value then dividing the sum by 2.
- midrange = max value + min value/2
ROUND OFF RULE
Carry one more decimal than is present in the original set of values. Only to be used in the final calculation. EX the mean of 80.4 and 80.6 is 80.50 or the mean of 2,3,5 is 3.3333 or 3.3 on3 more decimal point than the original.