Data 205 Lab Assignment:

Unit 8 Correlation Lab (38 points)

Exercise 1: Dataframe Output and Measures of Central Tendency (12 points)

The dataset for this assignment come from a DATA 205 gradebook from an earlier semester and show the average scores for each student for the pretest, Perusall readings, labs, and test. They also include nolab and notest, variables which show whether students received or did not receive credit for the labs and test, respectively.

Dataset Structure

## tibble [107 x 6] (S3: tbl_df/tbl/data.frame) ## $ pretest : num [1:107] NA 0.44 0.31 0.44 0.31 0.25 0.19 0.25 0.13 0.19 ... ## $ perusall: num [1:107] 0.46 0.845 1 1 0.378 ... ## $ labs : num [1:107] 0 0.925 0.805 0.887 0.333 ... ## $ test : num [1:107] 0.682 0.932 0.773 0.75 0 ... ## $ nolab : Factor w/ 2 levels "credit for lab",..: 2 1 1 1 1 1 1 2 1 1 ... ## $ notest : Factor w/ 2 levels "credit for test",..: 1 1 1 1 2 2 1 2 1 1 ...

Summary Statistics

## pretest perusall labs test ## Min. :0.0000 Min. :0.0000 Min. :0.0000 Min. :0.0000 ## 1st Qu.:0.2800 1st Qu.:0.3523 1st Qu.:0.2167 1st Qu.:0.0000 ## Median :0.4400 Median :0.8201 Median :0.5806 Median :0.6591 ## Mean :0.3994 Mean :0.6461 Mean :0.4922 Mean :0.4749 ## 3rd Qu.:0.5000 3rd Qu.:0.9879 3rd Qu.:0.7694 3rd Qu.:0.7727 ## Max. :0.7500 Max. :1.0000 Max. :0.9567 Max. :0.9773 ## NA's :20 NA's :14 ## nolab notest ## credit for lab :85 credit for test :69 ## no credit for lab:22 no credit for test:38 ## ## ## ## ##

1. How many students are in the dataset? How many variables?

2. Which variables are categorical? Which are numeric?

3. What is the range of lab grades? What is the range of test grades?

4. The summary output shows the number of NA's at the bottom of the column for pretest and for perusall. NA is the code that R uses to show that a value is missing. How many students are missing grades on Perusall?

5. The only way to receive a zero average for the labs is to fail to hand in any assignments. (No one handed in all three assignments and received zero credit.) However, the zero on the test score could reflect that a student didn't take or hand in the test or didn't get any answers correct (highly improbable). Some students have zeroes for both their lab grades and their test grades. These students may have dropped out of the class.

5A. What would happen to the mean of test grades if we removed the students who have dropped the class from the data?

5B. Does it make sense to include the scores for students who have dropped the class in the test grade data if we want to understand the distribution of test scores? Why or why not?