scientific theory

Sample Assessment Name: __________________________

It has been suggested that antibacterial soap kills more bacteria on hands than standard hand soap so a researcher is interested in finding out if is accurate. He randomly assigned participants to one of two experimental groups. Each individual first made a control plate by swabbing his/her unwashed hands with a sterile cotton swab and then carefully transferred the bacteria on the swab to a Petri dish containing nutrient agar. Upon completion of the control plate, individuals assigned to group “A” used soap “A” to conduct a standard hand wash. Individuals assigned to group “B” used soap “B” to conduct a standard hard wash. All individuals then swabbed their hands after hand washing and carefully transferred the bacteria on the swab to a second Petri dish containing nutrient agar. All samples were incubated for 48 hours and the number of colonies of bacteria in each condition were counted. Below is a table of a portion of the data collected.

Control plate colony count	“A” soap colony count	“B”soap colony count
58	21	18
44	13	12
72	18	20
25	10	11
47	7	4

State the null hypothesis:

__________________________________________________________

State the alternative hypotheses (there are several):

________________________________

________________________________

________________________________

What is the independent variable? __________________

What is the dependent variable? ___________________

1. In the table above, calculate the mean colony count for each condition (control, A, B). The mean is calculated by adding all the numbers in each column and dividing by the total number of data points (e.g. add all numbers in first column for the control condition and divide by 5).

Control mean = ___________

“A” condition = ___________

“B” condition = ___________

2. Make a bar graph of mean colony counts (one bar for each mean condition). Be sure to label the axes of your graph and to identify units (IV on x axis, DV on y axis).

3. Describe the relationship between the number of colonies comparing each soap condition to the control and then comparing the two soap conditions to one another. Does this data support the researcher’s null hypothesis?

4. Let’s say the researcher counted the number of bacterial colonies formed for condition “A” and condition “B” and found that they were just about equal. Based on this finding, does the data above support the researcher’s null hypothesis? Explain why or why not.

5. Make a graph similar to the one you made for Question #2, but this time draw a bar graph representing mean data that would not support the researcher’s null hypothesis if the participant’s hands after handwashing in soap “A” had half the amount of bacterial colonies as originally found and twice as many bacterial colonies for soap “B” as originally found.