## Lab Assignment 1 Introduction to SPSS: Descriptive Statistics

### statistics

##### Description

INSTRUCTIONS: This assignment will allow you to practice calculating and interpreting descriptive statistics using SPSS. You should review Chapters 1 and 2 of "A Student Guide to SPSS" before trying to complete this assignment. Use the SPSS file 'Assignment 1 Data.sav’ to complete the assignment. This file can be found in the 'Laboratories' folder on Connect. The data contained in the SPSS file are from the Stroop experiment your class completed using CogLab.

Marking of lab assignments will be very strict. If you did not complete the CogLab experiment on time, you will lose 1/4 of the total assignment grade (7 points). To avoid receiving other deductions, type your answers in the spaces provided. You may insert additional spaces after any question as needed. In addition, use proper symbols and notation (e.g., , s2, z) in all your answers, and properly round all your answers to 2 decimal places. You will lose marks for each and every failure to follow these directions.

This lab assignment is due at the beginning of class on Thursday, January 26. You must print out your completed assignment. Do not email your assignment. You will lose 1/8 of the total assignment grade (4 points) for each day it is late. An assignment will be considered one day late as soon as the lecture begins on the due date. Please follow the instructions on Connect if you are late.

Begin by opening the SPSS file. You will find three variables in the file: CogLabID, rtsame, and different. The variable labeled 'CogLabID' shows subjects' CogLab User IDs. The variable labeled 'rtsame' represents subjects' mean reaction times (rt) on congruent trials. Congruent trials are those for which the color of the word matched the word itself (e.g., the word RED was printed in red ink). The variable labeled 'different' represents subjects' mean reaction times (rt) on incongruent trials. Incongruent trials are those for which the color of the word did not match the word itself (e.g., the word RED was printed in blue ink).

Using SPSS, calculate descriptive statistics on the Stroop 'different' variable, and answer the following. [9 points]

Report the mean (0.5 points)d.   Report the range  (0.5 points)

Report the median (0.5 points)e.   Report the standard deviation  (0.5 points)

Report the mode (0.5 points)f.   Report the variance  (0.5 points)

Based on the values you reported in the preceding answers, what can you conclude about the shape (specifically, symmetry vs. skew) of the distribution of the different variable? (1 point) Explain your answer. (2 points).

Based on your answer to part 1g, which is the most appropriate indicator of central tendency to use for descriptive purposes (1 point)? Provide an explanation for your conclusion (2 points).

Using SPSS, calculate the median and standard deviation for the Stroop 'rtsame' variable, and answer the following. [4 points]

Report the median. (0.5 point)

Report the standard deviation. (0.5 point)

Which variable has a higher standard deviation: 'different' or 'rtsame'? (0.5 point)

Are you surprised by your answer to question 2 c? Why or why not? (1 point) [It might help to read a bit about the experiment in the CogLab manual to answer this question. If you purchased CogLab online, you can find a free PDF copy of the “Student Manual” for download at the CogLab website, under the “Help” tab.]

Which variable has a higher median: 'different' or 'rtsame'? (0.5 point)

Interpret the standard deviation of the 'rtsame' variable. [Hint: I am looking for more than  “the standard deviation is a measure of variability or dispersion”. A precise interpretation would make reference to the actual value of the standard deviation.]  (1 point)

Using SPSS, compute a new variable reflecting participants' interference scores (the amount of interference the meaning of the words creates on subjects' reading speed). Subtract participants' reaction time (rt) on congruent trials from their rt on incongruent trials ('different' – 'rtsame'), label the new variable 'as interfering,' and answer the following. [6 points]

Report the mean (0.5 point)d.   Report the range  (0.5 point)

Report the median (0.5 point)e.   Report the standard deviation  (0.5 point)

Report the mode (0.5 point)f.   Report the variance  (0.5 point)

What percentage of students was faster at responding to words in an incongruent ink color ('different') than to words in a congruent ink color ('rtsame')? (1 point)

Using SPSS, convert the 'as interfere' variable scores from milliseconds to seconds (by dividing them by 1000). Call the new variable 'interfere.' Use SPSS to calculate the mean, median, range, and standard deviation of this new variable. How did the conversion affect the mean, median, range, and standard deviation of the original 'as interfere' scores? (1 point) Why did it have this effect? (1 point)

Using SPSS, transform the 'as interfere' variable scores to z scores (be sure to do this using SPSS), and answer the following. [9 points]

Report the mean and standard deviation of the set of z scores. (1 point) Do your answers surprise you? Why or why not? (1 point)

Report subject Truong2017-49’s z-score. (1 point)

Provide a precise interpretation of Truong2017-49’s z-score. [A precise interpretation would make reference to the actual value of the z score.] (2 points)

What is Truong2017-49's percentile rank? Be sure to use SPSS to get your answer, and report the percentile rank to two decimal places. (2 points) Provide a precise interpretation of this percentile rank. [A precise interpretation would make reference to the actual value of the percentile rank.] (2 points)