## Which hypothesis test should I use?

### Identifying variables is necessary before you can make a hypothesis.

A research **How To Develop Hypotheses For Research** hypothesis is the statement created by researchers **How To Develop Hypotheses For Research** when they a realistic and testable hypothesis around which they can build the experiment.

### There is usually one hypothesis for each question you have.

The solution LOTH offers for what I called the problem of thinking,above, is connected to the argument here because the two phenomena areconnected in a deep way. Thinking requires that the logico-semanticproperties of a *particular* thought process be somehowcausally implicated in the process (say, inferring that Johnis happy from knowing that if John is at the beach then John is happyand coming to realize that John is indeed at the beach). The systematicity of inferentialthought processes then is based on the observation that if the agentis capable of making *that* particular inference, then she iscapable of making many other somehow *similarly* organizedinferences. But the idea of similar organization in this context seemsto demand some sort of classification of thoughts independently oftheir *particular* content. But what can the basis of such aclassification be? The only basis seems to be the logico-syntacticproperties of thoughts, their form. Although it feels a little uneasyto talk about syntactic properties of thoughts common-sensicallyunderstood, it seems that they are forced upon us by the very attemptto understand their semantic properties: how, for instance, could weexplain the semantic content of the thought that if John is at thebeach then he is happy without somehow appealing to its being a*conditional*? This is the point of contact between the twophenomena. Especially when the demands of naturalism are added to thispicture, inferring a LOT (= a representational system satisfying B)realized in the brain becomes almost irresistible. Indeed Rey (1995)doesn't resist and claims that, given the above observations, LOTH canbe established on the basis of arguments that are not “merelyempirical”. I leave it to the reader to evaluate whether mere criticalreflection on our concepts of thought and thinking (along with certain mundane empirical observations about them) can be sufficient to establish LOTH.^{[]}

A **null hypothesis** (H0) exists when a researcher believes there is no relationship between the two variables, or there is a lack of information to state a scientific hypothesis. This is something to attempt to disprove or discredit.

## In order for a hypothesis to be sound, hold tight to these tips:

The probability that was calculated above, 0.030, is the probability of getting 17 or fewer males out of 48. It would be significant, using the conventional *P**P*=0.03 value found by adding the probabilities of getting 17 or fewer males. This is called a one-tailed probability, because you are adding the probabilities in only one tail of the distribution shown in the figure. However, if your null hypothesis is "The proportion of males is 0.5", then your alternative hypothesis is "The proportion of males is different from 0.5." In that case, you should add the probability of getting 17 or fewer females to the probability of getting 17 or fewer males. This is called a two-tailed probability. If you do that with the chicken result, you get *P*=0.06, which is not quite significant.

## H0: Null hypothesis (no change, no difference);

How likely it is to observe a sample mean of 192.1 or higher when the true population mean is 191 (i.e., if the null hypothesis is true)? We can again compute this probability using the Central Limit Theorem. Specifically,

## H1: Research hypothesis (investigator's belief); α =0.05

You must choose your significance level before you collect the data, of course. If you choose to use a different significance level than the conventional 0.05, people will be skeptical; you must be able to justify your choice. **Throughout this handbook, I will always use P** If you are doing an experiment where the cost of a false positive is a lot greater or smaller than the cost of a false negative, or an experiment where you think it is unlikely that the alternative hypothesis will be true, you should consider using a different significance level.

## We reject the null hypothesis because -6.15

You should decide whether to use the one-tailed or two-tailed probability before you collect your data, of course. A one-tailed probability is more powerful, in the sense of having a lower chance of false negatives, but you should only use a one-tailed probability if you really, truly have a firm prediction about which direction of deviation you would consider interesting. In the chicken example, you might be tempted to use a one-tailed probability, because you're only looking for treatments that decrease the proportion of worthless male chickens. But if you accidentally found a treatment that produced 87% male chickens, would you really publish the result as "The treatment did not cause a significant decrease in the proportion of male chickens"? I hope not. You'd realize that this unexpected result, even though it wasn't what you and your farmer friends wanted, would be very interesting to other people; by leading to discoveries about the fundamental biology of sex-determination in chickens, in might even help you produce more female chickens someday. Any time a deviation in either direction would be interesting, you should use the two-tailed probability. In addition, people are skeptical of one-tailed probabilities, especially if a one-tailed probability is significant and a two-tailed probability would not be significant (as in our chocolate-eating chicken example). Unless you provide a very convincing explanation, people may think you decided to use the one-tailed probability *after* you saw that the two-tailed probability wasn't quite significant, which would be cheating. It may be easier to always use two-tailed probabilities. **For this handbook, I will always use two-tailed probabilities, unless I make it very clear that only one direction of deviation from the null hypothesis would be interesting.**