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Lecture 3

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Department
Psychology
Course
PSY201H5
Professor
Bruce Schneider
Semester
Fall

Description
Example: The percentile: draw a verticle line where it intersects this function from 80 y axis and 5 on x-axis we know its from 78-80 we want something more precise: Linear relationship This is not accumulative distribution: we don’t know precisely what the value is …what we rep. Linear approximation of this cumulative freq histogram which we used to find the percentile rank of the score… - if we have a line btw these two points: whats the equation: y=mx + b = this is the equation of the straight line: we know btw these two limits …there is a straight line that describes the relationship btwn them -have to know the value of the slope and the intersect: you just plug intot he equation and u get y -how do u find the value of the slope: you use the two points and look at the difference btwn the y and x values= gives u slope of the line Slope of the line is = upper value of the y / lower value of y Y a • 4.95 uppoer point, lower point 3.45 -Look at slide 14 once we have the quation m = (82.18-64.36)/(4.95-3.45) = 11.88 • b = 82.18 – 11.88*4.95 = 23.374 we can plugin the value of X to get Y = 79 another way of doing LINEAR interpretation: slide #15 • m = (y U y )L(x –Ux ) L • m = (y P y )L(x –Px ) L • (yU– y )L(x U x )L= (y –Py )/Lx –Px )LEQUATE THEM since both give u value of slope Slide 15: answer 79.21 ( SAME way but different mathematical expression) LINEAR interpleation** THIS IS THE FORMULA that we are going to use If you have a particular score, historgram than u can use this to find percentile rank of any score PERCENTILE POINT: Find out what score corresponds to the 98 percentile etc.. or 30 percentile etc… eg. 75 th go to graph and locate it (see slide 16) When we go in opp direction still have to determine slope and intersect: find slope of that line by finding m (slide #20) We are saying 4.3 is 70 percent percentile To check you go back to original data and find out: slide #21 check answer #slide 22 Suppose you were quarter master for Canadian- you need uniforms that roughly fits the groups…how do u do that?what do u need to do inorder for u to do that: size – compute the percentage of the sizes…know what percentage lie btw the values: find percentage of scores etc… th If your going to graduate school requires 85 percentile graduate record design: what score responds in correct percentile: u can go through practice to try and boost ur score up..u need to know what the score is You want to see how generaous UTM undergrads are slide #26= score rep that persons generosity that would accurately reflect what the person would do in real life: CENTRAL TENDENCY: we want a single number that represents them well: we need a more precise definition: we know how to calculate it and if we communicatre it to someone else they know what we did: 3 sep measure of central tendency: The mode all u have to do is identify the most frequent tendency: Mode can be unambiguously defined: 2 peak distribution, peak 1 the mode is such and such, peak 2 the mode is such and suck Know the difference btw sample mean: Xbar or Ybar - expected value is equal to the populatio
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