AP BIO UNIT 1 (STATS)

Null hypothesis (H0)

states that there is no statistically significant difference between two groups in a experiment.

Chi-Squared Test

a statistical test that is used to compare the observed results to the expected results in the experiment.

-used to evaluate the null hypothesis

-used in genetics problems

Chi-Squared Test Example

It would be appropriate to compare the number of purple flowers and the number of white flowers that resulted from genetic crossing but would not be appropriate if it was for percentages of those flowers

Chi-Squared Formula

Summation (Observed-Expected) squared/expected

Expected

prediction

Observed

what actually happened

Degree of Freedom (df)

defined as the number of possible outcomes in an experiment minus 1

Chi-Squared steps

1. Calculate Chi-Squared value using the formula

2. Determine the degrees of freedom

3. Use the degrees of freedom and the p-value and find the critical value in the chi-squared table

4. Compare Chi-Squared value to critical value

5. Based on comparison respond with either reject or fail to reject null hypothesis

P-Value

defined as the probability that the observed data would be produced by random chance alone

Fail to reject null hypothesis

Chi-Squared is less than or equal to critical value

Reject Null hypothesis

Chi-Squared is greater than the critical value

mean

average

median

middle

Standard Deviation

averages how far each data point is from the mean of the data set

Standard error of the mean

measure of how spread out the data set is

sample size increases

standard error of mean decreases

95% confidence interval

if you repeated an experiment 100 times and calculated the mean of the data you collected each time, the mean would fall within the 95% confidence interval 95 of those 100 times.