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Lecture 3

Winter Week 3 - Descriptive/Bivariate Statistics

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School
Department
Nursing
Course
NUR 80A/B
Professor
L.Atack
Semester
Fall

Description
Winter Week 3 DescriptiveBivariate StatisticsFebruary1311502 PMVariabilityWhy study variabilityKnowing the average score for a test or measure is useful but it does not tell the whole story Its one thing to know the class average was 72 Its also important to know where most peoples scores on that test fell as well that is variabilitythe spread of scoresVariability reflects how scores differs from the mean averageLets say you entered a swimming contest which included swimmers with a range of abilities and the average score was 710 That sounds good but what would you think of the judging if everyonegot a 710 Together average and variability can be used to describe the characteristics of a distribution and show how distributions differ from one anotherWhen you read nursing research expect to see the average and a variability test result reportedVariability measures the degree to which scores in a distribution are spread out or dispersedhomogeneitylittle variabilityheterogeneitygreat variabilityThis can be done using three measures of variability spread or dispersion in a group of scores the range standard deviation SD and the varianceRangeThe most general measure of variability used almost exclusively to get a very general estimate of how wide or different scores are from one another That is the range shows how much spread there is from the lowest to the highest point in a distributionIt gives you an idea of how far apart the scores are from one anotherShould not be used to reach any conclusions regarding how individual scores differ from one anotherUsually seen as one of several measures of variabilityCalculating the RangeTo calculate the rangeSubtract the lowest score in a distribution from the highest score in the distributionFormula rh lrrange hhighest score llowest scoreExample17 23 27 16 22 24 16 23 18 23 19 22 23 25r27 16r11Advantages and Disadvantages of the Rangemost obvious way of describing how spread out scores are howeverit is determined by the two extreme values and ignores the other scores in the distributiontypically used with not instead of other measures of variabilityStandard Deviation SDMost commonly used and most important measure of variabilityRepresents the average amount of variability in a set of scores Its the average distance from the mean The larger the SD the larger the average distance each data point is from the mean of the distribution heterogeneous the more different the values are from one anotherAlso very sensitive to extreme scoresAllows us to compare scores between different groupsCalculated using every score on a distributionCalculating the Standard Deviation Research Page 1
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