IB Bio SL Unit 1 Statsitics

What is a t-test?

* It is used to determine if a statistical difference exists between the means of 2 populations. It also determines the degree of overlap between two sets.
* If there is no overlap, they’re statically different and vice versa.
* If the critical value (p value) is smaller than 0.05, the null hypothesis is accepted and if the p value larger than 0.05, than the null is rejected and the alternative is accepted.

What does a small and large standard deviation signify?

Small: Data is closely clustered around the mean value

Large: Data is widely spread around the mean value

What’s the purpose of calculating standard deviation?

To measure the spread of values around the mean. This will tell the researcher if the results from the experiment are consistent or not.

What is an error bar?

A method of representing the standard deviation or range of data in a graph

What percent of values of a normal distribution fall?

1SD: 68%

2SD: 95%

3SD: 99.7%

Null hypothesis

States that there will be no statically significant difference between the two means (t-test) and no difference between observed and expected (chi squared)

Alternate hypothesis

States that there will be a statistically significant difference between the means (reject null to accept alternate, t-test) assumes a statically significant difference between observed and expected values

The level of significance (probability value, p) for the t-test is always… (you are __ confident that results are related to the IV)

0\.05 or 95%

What’s Chi-Squared?

It is used to determine how far data you observe deviates from what you expected. If the critical value (p-value) is smaller than the chi squared value (0.05), the null hypothesis is rejected and if the critical value is larger, than it is accepted.

How do you calculate the degrees of freedom?

(number of levels) - 1