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Unformatted text preview: STA 2122 Glossary: Sections 1.1 – 1.2 Descriptive statistics organize and summarize the data. Inferential statistics are used to make predictions and decisions about a population based on information from a sample. Sections 1.3 An experimental unit is the individual or object on which a variable is measured. The population is the set of all measurements of interest to the investigator. A sample is a subset of measurements selected from the population of interest. A variable is a characteristic that changes or varies over time or varies across different individual subjects. A measure of reliability is a statement about the degree of uncertainty of a statistical inference. Section 1.4 Quantitative variables are numerical observations. Qualitative variables are non-numerical or categorical observations. Section 1.5 A representative sample exhibits characteristics typical of the target population. A random sample is selected in such a way that every different sample of size n has an equal chance of selection Section 2.1 A class is one of the categories into which data can be classified. Class ~ Category Class frequency is the number of observations belonging to the class. Relative Frequency = Frequency n 1 Class percentage = (Class relative frequency) X 100 A Pareto Diagram is a bar graph that arranges the categories by height from tallest (left) to smallest (right). Section 2.2 A relative frequency distribution (or frequency table ) lists data values (usually in groups), along with their corresponding relative frequencies . “Relative” here refers to our sample size (n). Also, “Frequencies” is just another way to say counts. Relative Frequency = Frequency n In a relative frequency distribution each data value belongs to an interval of numbers called a class . Each class has a lower and upper class limit that define the interval. Lower class limits are the smallest numbers that can belong to the different classes. Upper class limits are the largest numbers that can belong to the different classes. Example - In the BCC employee example below, the lower class limits are 1, 6, 11, 16, 21, and 26, and the upper class limits are 5, 10, 15, 20, 25, and 30. Class boundaries are the numbers used to separate classes, but without the gaps created by class limits. They are obtained as follows: Find the size of the gap between the upper class limit of one class and the lower class limit of the next class. Add half of that amount to each upper class limit to find the upper class boundaries; subtract half of that amount from each lower class limit to find the lower class boundaries. Example - Find the class boundaries for the BCC employee example. Class midpoints are the midpoints of the classes. Each class midpoint can be found by adding the lower class limit to the upper class limit and dividing the sum by 2....
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