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I did an experiment and had one independent variable and 2 dependent variables. Basically I tested diff. concentrations of an inhibitor on an enzyme and determined the enzyme's activity by measuring change in pH and temp. I know for a fact that the inhibitor will decrease the enzyme's activity and decrease it only so it's 1-tailed.

I don't understand the t-test. I also heard there's ANOVA which one should I be doing? And how? I've calculated the mean change in pH and temp. for 5 enzyme concentrations also the standard deviation. I do not know what to do with the data

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The t test is used when you have just two conditions (two means) to compare. ANOVA is for comparisons of more than two conditions (more than two means). The t test is a special case of ANOVA. For two conditions (two means), t test and ANOVA yield the same p-value for the test of equality of the two means.

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Probably neither one.

You say you have five enzyme concentrations and want to look at how they are related to change in pH and temperature. You also say that these measure enzyme activity (although you don't say how they do that).

But let's take one example: Change in temperature. If you are really interested in change in temperature (and don't care about initial temperature -- maybe all were at the same temp. at the beginning) then you want regression. Although ANOVA and regression are the same model, mathematically, ANOVA is used only when the IV is categorical. Yours is not.

If the samples started at different temperatures, then you have a repeated measures problem, which is more complex.

You may have a repeated measures problem for other reasons as well (e.g. if the samples are different from each other).

I would suggest that you hire a consultant to help you with this. Or, at least, take a couple courses in statistics at grad school.

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