Accessing quantitative data see the technology detour

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Accessing quantitative data: See the Technology Detour after Investigation 1.1 for instructions on how to load data into R/Minitab. Remember to search the help menus for more information if you have more complicated data files in the future. R Notes: Recall that the + sign comes up in R after you hit Enter when R is expecting the next line to be a continuation of the previous line. You can alternatively continue the command on the same line. In the instructions below, some steps are optional, but we wanted you to know they were there. You should get into the habit of “attaching” the data once it has been read in to R . Minitab Notes : The file is too large to copy and paste from the webpage, so save the file to your computer and use File > Other Files > Import Special Text . Specify C1-C7 for storing the data and then press Format . Select the Tab delimited option and press OK twice. Change file extension to .TXT Check that you have 324,314 rows of data.
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Chance/Rossman, 2015 ISCAM III Investigation 2.1 137 Now use technology to create a dotplot of the birth weights. Technology Detour Dotplots In R Assuming you imported the data into “births” > attach(births); names(births) ± Shows the variable names for your data > iscamdotplot(birthweight) ± Input quantitative variable (after attaching) In Minitab x Choose Graph > Dotplot . x Select One Y, Simple option. x Press OK . x Double click on the C2 birthweight listing in the left window so it appears in the Graph variables box (or type C2 or seconds directly into the Graph variables box). Press OK . (c) Describe what you see. Discussion: The observations at 9999 don’t seem to belong. The “ codebook ” for these data states that the largest birth weight is 8165 grams and for other variables it lists 99, 999, 9999 as values for “not st ated” or unknown. You could convert these observations to the missing value designator in your software (e.g., * in Minitab and NaN in R) or you can create a new data set that does not include those rows. Technology Detour Subsetting the Data In R > births2=births[which(birthweight < 9999), ] ± selects rows that satisfy condition ± notice the comma! > attach(births2) ± “birthweight” now refers to these data Or, you can refer to the new data using births2$birthweight In Minitab x Choose Data > Subset Worksheet x Specify C2 as the column you want to condition on x Change the condition to “is less than” x Use 9999 as the value, uncheck “Include value” x Press OK . x You should get a new worksheet “c2 less than 9999”
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Chance/Rossman, 2015 ISCAM III Investigation 2.1 138 (d) Recreate the dotplot with the subsetted data and describe what you see. It may still be difficult to see much in the dotplot with such a large data set, especially if there are many distinct (non- repeated) values. One solution is to “bin” the observations. Some software packages (e.g., Minitab) will do that automatically even with a dotplot. Another approach is to use a different type of graph, a histogram, that groups the data into intervals of equal width (e.g., 1000-2000, 2000- 3000, …)
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