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Unformatted text preview: Using Statistics to Answer Questions Chapter 9 Statistics : Branch of mathematics that involves the collection, analysis, and interpretation of data. o Two main branches of statistics assist your decisions in different ways. Descriptive Statistics Procedures used to summarize a set of data. Measure of central tendency : typical or representative score Variability : what spread exists in the scores Inferential Statistics Inferential statistics are used to analyze data after you have conducted an experiment to determine whether your independent variable had a significant effect. Scales of Measurement Measurement : The assignment of symbols to events according to a set of rules. Scale of measurement : A set of measurement rules o Nominal Scale Events are assigned to categories, classify your research participants as men or women, as righthanded or lefthanded, as Catholic or Protestant. Differences between categories are qualitative (kind) and not quantitative (degree). Do number of individuals in one category differs as a function of some treatment? Examples: Jersey numbers, telephones, zip codes? o Ordinal Scale Permits events to be rank ordered ; usually single continuum that underlies a classification system Examples: college football standing, pop music charts, class standings, might divide participants up on basis of creativity and end up with three categories (noncreative, creative, highly creative) Degree of quantitative difference that nominal scale does not have Differences between consecutive values are not necessarily equal: Ex. top 20 football teams (difference between 1 and 4, not necessarily same as 6 and 9) dont know how much distance exists between ranks. o Interval Scale Rank ordering and assumption of equal distance between ranks; household thermometer, ACT, SAT, often chosen because no true zero . o Ratio Scale Rank ordering of events, assumption of equal distance between ranks and a true zero point ; weight, length, calorie content of food o Scales of measurement directly determine which measure of tendency you will use. Measures of Central Tendency Mode o The score in distribution that occurs most often; can be more than one mode o 12, 15, 20, 20, 20 o Mode is 20 o Only measure of central tendency that can be use for nominal data Median o The number that divides a distribution into equal halves, to calculate first rank them o 56, 15, 12, 20, 17 o 12, 15, 17, 20, 56 (Median is 17) o for ordinal, interval, and ratio data Mean o The arithmetic average of a set of numbers. It is found by adding all the scores in a set and then dividing by the number of scores....
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 Spring '11
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