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Descriptive Statistics Introduction to Study Skills & Research Methods (HL10040) Dr James Betts

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Lecture Outline: Statistics Variables Levels of Measurement Measures of Central Tendency Distribution Variability.

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StatisticsDescriptiveInferentialCorrelational

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Nominal Scale Ordinal Scale

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Interval Scale Ratio Scale

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Quick Test Nominal, Ordinal, Interval or Ratio? –Blood lactate concentration (mmol.l -1 ) –Profile of Mood States (scale 1-7) –Heart Rate (beats.min -1 ) –Blood Group –Bench Press 1RM (kg) –Year of Birth (AD) –Atmospheric Pressure (mmHg)

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Système Internationale (SI) Units Seven constant * base units using the metric system VariableUnitSymbol Accepted Derivations Distancemetrem ha for area; º for angle; # l or L for volume Mass * kilogramkgt Timesecondsmin, h, d (not year) TemperaturekelvinK Molemolemol # l or L for volume CurrentampereA Luminancecandelacd Units always lower-case #, neither italicised nor pleuralised (i.e. kg not KGS) and with space between value and unit (inc. % but exc. º).

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Discrete and Continuous Variables Discrete Variables: Continuous Variables:

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Indicators of Central Tendency Mode –Most Frequently Occurring Score Median –Middle Score Mean –Arithmetic Average.

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Normal Distribution

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Non-Normal Distribution

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Hypothetical Investigation The effect of 1 week placebo supplementation on press-up performance 8 randomly sampled participants Performed as many press-ups as possible Supplemented with placebo tablets for 1 week Performed as many press-ups as possible

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Mean SD

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68.26% Number of Press-ups ????????????????????????????????????????????????????? Standard Error of the Mean (SEM)

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SEM = SD n

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Mean SEM

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The mean SD or SEM cannot be used for non-normally distributed data Instead the median is often plotted along with either the range or the IQR Raw Data: 8, 10, 15, 20, 55, 75, 120, 179 Median & Range or IQR

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Put the data from each trial into SPSS… Week 1 Week 2

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Select Analyze, GLM, Repeated Measures…

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Move variables from here… …to here, click ok

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ANOVA Output nCI = MSE n [criterion t (df)]

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t – Distribution Table Critical t-ratio Degrees of Freedom (Google Search)

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Mean nCI

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Selected Reading Hopkins W. G. (2000) A New View of Statistics [Online] Auckland: Internet Society for Sport Science. Available at: [accessed October 3rd 2005] Masson, M. E. J. and G. R. Loftus. Using confidence intervals for graphically based data interpretation. Canadian Journal of Experimental Psychology. 57: , 2003.

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