Question 1:

A usability analyst is interested in evaluating an ATM interface.
She decides to conduct an experiment and selects a random sample of 
twenty-five users for observation. She provides them with a suite of 
tasks and observes the time to complete the task suite. She discovers 
that the mean time is 150 seconds with standard deviation 30.

Given these facts, answer the following questions. Remember to make and  
state any necessary assumptions in each case.

a) Provide a point estimate for the population mean.
b) Determine the error in your estimate of the population mean.
c) Construct and interpret a 90% confidence interval for the population 
   mean. 
d) Construct and interpret a 95% confidence interval for the population 
   mean. 
e) Determine the minimum sample size needed to estimate the population 
   mean to a level of accuracy of 2 seconds with 99% confidence.


Question 2:

A software training consultant disagrees with the widely held
notion that training casual users of basic software tools like
Wordprocessors and Spreadsheets is ineffective. She believes 
that a short training session can dramatically improve the 
efficiency of casual Microsoft Word users and decides to 
conduct an experiment to investigate this issue.

She randomly selects two groups of casual Microsoft Word users 
from her organization and decides to use one group as a Control 
group and the other group as a Treatment group. That is, the 
Control group will not receive training but each member in the 
Treatment group will receive a short training session on various 
Microsoft Word features. 

She assigns a suite of tasks to each individual in each group 
and records the time required to complete the suite.  

a) Given the problem statement above, identify and state the 
   null and alternative hypotheses. 
b) Let us say that the following statistics are available:
   Control Group: n=49; ybar=56; s(y)=18
   Treatment Group: n=64; ybar=50; s(y)=20
   Given these details and your hypotheses, conduct a test of 
   hypotheses. 



Question 3:

You are interested in comparing two different techniques (say 
method a and method b) that may be used to conduct software 
inspections. Many of your colleagues argue that the techniques
are equally effective but, based on personal experience, you 
contend that method b is better than method a and decide to 
design an experiment to settle the matter. 

To evaluate the methodologies you decide to randomly select 
two groups of programmers from your software development 
team. You train each group on one of the techniques and then 
give them a few days to get comfortable with the technique. 
Each programmer is then given a suite of modules to inspect 
and the number of software bugs detected is recorded. 

a) Given the problem statement above, identify and state the 
   null and alternative hypotheses. 
b) Let us say that the following statistics are available:
   method a: n=36; ybar=18; s(y)=6 
   method b: n=36; ybar=23; s(y)=4
   Given these details and your hypotheses, conduct a test of 
   hypotheses. Remember to comment on the respective techniques.


Question 4:

A usability analyst has been hired by a software consulting firm
to compare the effectiveness of a new ATM interface (GUI#1) and an 
existing interface (GUI#2). The consulting firm must convince the 
client that the new interface will allow experienced internet 
users to complete tasks more quickly. 

The analyst selects a random sample of twenty-five users for 
observation. She provides them with a suite of tasks and records
the time each user takes to complete the task suite for each
interface. To account for the learning effect, the analyst 
randomly selects the interface that each user initially uses.
She then computes the difference in task completion time for each
user (i.e. GUI#2 - GUI#1) and discovers that the mean difference 
is 6 seconds with standard deviation 2.4 seconds.

Given the problem statement above, conduct a test of hypotheses. 
Remember to comment on the respective GUI's. 

Note: Make and state any necessary assumptions.