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I'm having trouble with a statistics question I did a hypothetical scatter plot of marijuana use and other drug use and came out with a correlation coefficient of 0.94, so there's a strong correlation with the data but for the second part it asks does the data confirm that marijuana is a "gateway

drug"? And I've so far answered that correlation doesn't necessarily mean causation, but I need to come up with an example of a third variable that could be effecting the results do you guys have any suggestions for a third variable that could be effecting the data?

Alcohol use.

Tobacco could also work.

If alcohol, tobacco, or both are excluded from the data you're using, you could also argue that their exclusion has artificially skewed the data.

Or SES

 Cheesecat wrote:
I'm having trouble with a statistics question I did a hypothetical scatter plot of marijuana use and other drug use and came out with a correlation coefficient of 0.94, so there's a strong correlation with the data but for the second part it asks does the data confirm that marijuana is a "gateway

drug"? And I've so far answered that correlation doesn't necessarily mean causation, but I need to come up with an example of a third variable that could be effecting the results do you guys have any suggestions for a third variable that could be effecting the data?

Do you have longitudinal data? If you have any kind of data concerning time...such as age of first marijuana use, you would be able to correlate age of first use with drug use later in life.

This is all very vague without seeing your dataset. Post up what variables you have available in your dataset if you want a serious response.


If not, you would use ANCOVA to analyze the covariance attributable to other variables of interest.

Alcohol is a great third variable. Just make sure its not already included in your "other drug use" variable. It is technically a drug so your data source may or may not have it in that category.

Even without another variable, correlation does not imply causation...

I thought he was just asking us for variables that could partially explain the relationship he found, not additional variables that would magically make it a causal relationship

Prescription drug abuse, assuming you can find data for it.

I can't vouch for anywhere else, but everyone I know knows at least one person (no, not me) that habitually abuses Vicodin. That's anecdote, I realize, but probably worth researching, and cheap enough to be prolific.


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 motyak wrote:
I thought he was just asking us for variables that could partially explain the relationship he found, not additional variables that would magically make it a causal relationship

Without knowing more details, it's hard to say. Arguably, a common use of drugs only shows a common use of drugs, not that pot is a gateway, anyway.

Also, it depends on if he's doing science, or trying to make a case for something.

I'm going to take a wild stab in the dark and guess that, from Cheesecat's ever so subtle avatar, he is trying to make a case for something.

 Corpsesarefun wrote:
I'm going to take a wild stab in the dark and guess that, from Cheesecat's ever so subtle avatar, he is trying to make a case for something.

Possibly. If so, the answer is still SES. It's almost always SES. SES is a golden answer for simple stats in regards to anything remotely illegal. And not simple as in simple slopes, those annoying things, simple like basic.

 Corpsesarefun wrote:
I'm going to take a wild stab in the dark and guess that, from Cheesecat's ever so subtle avatar, he is trying to make a case for something.

That's why I extended the possibility of the option.