lecture 1 - Tuesday ANNOUNCEMENTS First homework is already...

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Tuesday October 02, 2007 ANNOUNCEMENTS: First homework is already posted up on the web Work is not difficult Download ASAP Due a week from today beginning of class Every Tuesday you will be turning in some homework Put homework in a pile corresponding to your section 12:35 is when lecture will start www.timrichard.com/psych60 for syllabus and other useful information LECTURE 2: GRAPHS, AVERAGES DESCRIPTIVE STATISTICS Graphs 1. histograms 2
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a. weights of some people. Vertical axis is the frequency. Horizontal axis – the classes. We have a right skew. Comes out more in the right side than it does on the left side. You will be asked to make a histogram on homework 2. frequency polygons (image supplemented from world wide web) a. made same way as histogram, very similar. Histogram written in a different way. b. Instead of having rectangular classes. You create a polygon. You take the midpoints of each of the rectangles and then you connect the dots. c. When you make these histogram and frequency polygons you lose the RAW DATA. The individual data value. You cannot recreate the data from the histogram and frequency polygons. 3. stem and leaf displays a. refer to 2c. 3
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b. stem and leaf displays provides a visual representation of a histogram while preserving individual data. c. Ther are some MC questions and what a stem and leaf display is. d. Example: The following achievement score were obtained from a group of ….. you want to divide each number into a stem and a leaf 12|0 12|6 10|8 10|2 9|8 8|5 14|1 11|8 8|8 12|3 10|9 11|7 12|4 10|6 9|9 10|4 7|8 14|3 11|1 11|3 9|6 11|8 7| 8 8| 5, 8 9| 6, 8, 9 10| 2, 4, 6, 8, 9 11| 1, 3, 7, 8, 8 12| 0, 3, 4, 6 13| 14|1, 3 turn this 90 degrees counterclockwise and you will see a visual representation that looks like a histogram. It is just as useful as a histogram. 1| ####### you don’t want to have this kind of graph only one class 4
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100|0 – 199|9 (100 observations) Pick classes that are numerous enough to tell you data but don’t have too many observations 4. shape of distributions a. normal distributions-bell curve i. very popular shape ii. properties 1. symmetric with respect to the middle axis 2. half the data will be below the peak, half will be above the peak in theoretical shape 3. unimodal 4. there is no “skew” one tail DOES NOT go further than the other b. bimodal distribution i. not as popular as normal ii. [image of bimodal] iii. Generally the two modes does not have equal peaks. iv. Mixtures of two types of data. v. Example heights of a bunch of people. Half of them are infants say five people, the other half are adults 18+. This will give you a bimodel distribution vi. Occurs because of mixture effect vii. In most cases, you do not want this viii. If you do get it, you will find out something interesting is going on.
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