# Thread: One or Two Way ANOVA?

1. ## One or Two Way ANOVA?

Hi all,

Just had a quick question regarding whether or not I should be using a one or two way ANOVA to see the effect of caffeine on heart rate. My groups are: control, coffee, energy drink. My sample size is 50 for each group and for each individual I tested at the following times: initial, 30 mins., 60 min., 90 min., 120 min. after consumption.

My goal is to see if the experimental groups have a significant effect on HR but I'm unsure how to go about setting this up in Excel. Any ideas would be greatly appreciated.

2. ## Re: One or Two Way ANOVA?

hi,
I would go for two-way , one factor would be the drink, the other the time. I would be curious to see what you get.

regards

3. ## Re: One or Two Way ANOVA?

You could also consider Trend Analysis (using contrast coding) because your second factor is quantitative (time) with equal spacing i.e. initial, 30, 60, 90, 120.

4. ## Re: One or Two Way ANOVA?

You may also want to add group * time interaction to the mix to see if the effect of group on HR varies over time. For example, coffee may impact HR much later than an energy drink. I am not certain what Excel can handle (probably a 2-way ANOVA but unsure about interactions).

Also, were subjects randomized to each of the 3 groups? If not, there may be other differences between groups that affect heart rate for which you may need to control (covariates). Having different baseline HR between groups would be a particular concern. If subjects were randomized then baseline HR and covariate differences in general would likely be a non-issue.

5. ## Re: One or Two Way ANOVA?

Good points mostater. Also were interventions standardized. I believe there is quite a bit of variabilityin coffee options and energy drink options, along with sizes (fluid ounces). Without randomization as M pointed out, I can think of many issues (e.g., age, hydration, physical activity levels, social economic status, etc.) that could be grouped with choice.

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