Sarah S.
asked • 02/18/24i'm doing a study as a high schooler trying to see the effect of 2 different types of essential oils on e.coli. i'm kind of stuck not knowing which statistical tests are most appropriate.
What I did was that I increased the concentrations of the oils from 10% to 20%, 30%, 40%, and 50%. I used the disk diffusion tests and measured the inhibition zones formed. I also had a positive control being an antibiotic. In addition to that I combined the two oils in 5 different ratios to see if there's a synergistic effect. So if I'm not wrong, I've got 2 independent variables and 1 dependent variable.
Based off of what I've read online so far, there are one-way and two-way ANOVA tests, as well as t-tests, and Tukey's HSD test. I have never been more confused in my life and cannot tell which are the most relevant in my case. I also have no idea what method to use for measuring synergy.
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1 Expert Answer
Christal-Joy T. answered • 02/18/24
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Hey. If you have 2 independent variables with a positive control and 1 continuous DV, you are doing a one-way ANOVA. However, because you mentioned the usage of various treatments, you have the oils(3) being measured across the 5 different concentrations.
The addition of the treatments would make your model change from a one-way ANOVA to a mixed-model (or within-between ANOVA). These are most appropriate when you are examining for differences in a continuous level variable (the measurement of inhibition zones formed) by group (types of oil) and time (concentrations).
I hope this helps. Let me know if you have any additional questions.
Sarah S.
Hello, thanks for the reply. I still don't quite get what you mean. I thought a two-way ANOVA followed by tukey's HSD would fit best. Do you mind clarifying?
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02/19/24
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Callie R.
Given your experimental setup with two independent variables (concentration of oils and combination ratios) and one dependent variable (inhibition zone size), you have a few options for statistical analysis. Here's breakdown: One-way ANOVA: This test can be used to analyze the effect of one independent variable (concentration of oils) on the dependent variable (inhibition zone size) when you have multiple groups (different concentrations of oils). You can determine if there are significant differences in inhibition zone sizes among the different concentrations of oils. Two-way ANOVA: This test allows you to analyze the effects of two independent variables (concentration of oils and combination ratios) on the dependent variable (inhibition zone size). It can help you determine if there are main effects of each independent variable and if there's an interaction effect between them. T-tests: You can use t-tests to compare the means of two groups if you're specifically interested in comparing inhibition zone sizes between two specific concentrations of oils or two specific combination ratios. Tukey's HSD test: If your ANOVA results indicate significant differences between groups, Tukey's Honestly Significant Difference (HSD) test can be used as a post-hoc test to determine which specific groups differ significantly from each other. For measuring synergy in the combined ratios of oils, you might consider using a method such as the combination index (CI) method or the Bliss independence model. These methods compare the observed effect of the combination to the expected effect if the two oils were acting independently. Depending on the specifics of your experiment and data, you may need to consult with a statistician or conduct further research to determine the most appropriate method for assessing synergy in your particular case.02/29/24