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Lecture 3

# Lecture 3 - The Normal Curve and Standard Scores - September 27.docx

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Department
Psychology
Course
PSY201H1
Professor
Kristie Dukewich
Semester
Fall

Description
September 27, 2012. Lecture 3 – The Normal Curve and Standard Scores What is the Stroop?  Developed to explore the process of reading  Psychologists noticed that people named the colour of words faster if the colour names and colour of the letters were the same  People were slower if the colour of the letters was different from the colour name  Stroop interference occurs between………..  Congruent trial: colours match the words  Incongruent trial: colours do not match the words  Interference = incongruent reaction time – congruent reaction time Excel Commands  Mean o =average(____ - ____)  Median o =median(____ - _____)  Mode o =mode(____ - _____)  Range: Max-Min o =min(____ - ____) o =max(____ - ____) o =(Amax – Amin) for range 2 2 2  Variances: s = [sum of X – ((sum of X) /N)]/N – 1 o =VAR.S(___ - ___)  Standard Deviation (square root of variances) o =standard deviation (select variances) What’s so special about the mean?  Sensitive to all scores o If a score is changed the mean will always change because every score is used in its calculation, therefore…  Very sensitive to extreme scores o Many scores around the same value plus one extreme score will greatly change the average to an inaccurate extent o For this reason, median is better for extreme scores as it won’t change  Its deviation scores add to zero o Sum the deviation scores - o Sum of (X – X)  It’s squared deviation scores, when added, are the smallest you can get o Sum the squared deviation scores o Sum of (X – X)2  Least sensitive to weird samples when drawing from a population o This is the main reason why we use the mean as our primary measure of central tendency when calculating our inferential statistics o Studies use samples from the population o Every time we draw a sample, results won’t be exactly the same  If relied on median or mode, results would vary WILDLY  The mean is cool, typically not so sensitive to these sampling variations Central Tendency and Symmetry (in relation to above point #2)  Symmetrical “bell shaped” graphs  mean=median=mode 
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