Descriptive Statistics Introduction to Study Skills & Research Methods (HL10040) Dr James Betts
Lecture Outline: Statistics Variables Levels of Measurement Measures of Central Tendency Distribution Variability.
Statistics Descriptive Inferential Correlational
Nominal Scale Ordinal Scale
Interval Scale Ratio Scale
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)
Système Internationale (SI) Units Seven ‘constant’* base units using the metric system Variable Unit Symbol Accepted Derivations Distance metre m ha for area; º for angle; #l or L for volume Mass* kilogram kg t Time second s min, h, d (not year) Temperature kelvin K Mole mole mol #l or L for volume Current ampere A Luminance candela cd Units always lower-case#, neither italicised nor pleuralised (i.e. kg not KGS) and with space between value and unit (inc. % but exc. º).
Discrete and Continuous Variables Discrete Variables: Continuous Variables:
Indicators of Central Tendency Mode Most Frequently Occurring Score Median Middle Score Mean Arithmetic Average.
Normal Distribution
Normal Distribution
Normal Distribution
Non-Normal Distribution
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
Mean SD
Standard Error of the Mean (SEM) 68.26% ????????????????????????????????????????????????????? Number of Press-ups
Standard Error of the Mean (SEM) SD n SEM =
Mean SEM
Median & Range or IQR 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
Put the data from each trial into SPSS… Week 2 Week 1
Select ‘Analyze’, ‘GLM’, ‘Repeated Measures’…
Move variables from here… …to here, click ok
ANOVA Output MSE n nCI = [criterion t (df)]
t – Distribution Table Degrees of Freedom Critical t-ratio 1 2 3 4 5 6 (Google Search) Degrees of Freedom Critical t-ratio 1 2 3 4 5 6 7 8 12.71 4.30 3.18 2.78 2.57 2.45 2.37 2.31
Mean nCI
Selected Reading Hopkins W. G. (2000) A New View of Statistics [Online] Auckland: Internet Society for Sport Science. Available at: www.newstats.org [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. 57:203-220, 2003.