AP Biology and Statistics Statistics Statistics help to better - - PowerPoint PPT Presentation

AP Biology and Statistics

Statistics

• Statistics help to better understand the

meaning of a sample data set

• What do these numbers actually mean??

Data Analysis

• Data analysis allows you to:

–Arrive at conclusions about your data –Make claims about your data –Support arguments using your data –Estimate the reliability of your data –Effectively communicate conclusions about your work to a larger scientific community

Descriptive Statistics

• Appropriate descriptive statistics for a data set

typically include: –Mean (average) –Sample Size –Standard Deviation –Standard Error

Mean (Average)

Mean (Average)

• This formula should be used when you need

to calculate the average of a set of values (data points)

Mean (Average)

• Calculate the sample means of the two

environments, wet and dry

Standard Deviation

Standard Deviation

• This formula is used to determine the amount

by which your values (data points) typically differ from the mean value

• Trying to determine the amount of variation in

your data

Standard Deviation

Standard Deviation

High Standard Deviation (data points are spread out) Low Standard Deviation (data points are clustered)

Standard Deviation

• Calculate the standard deviation for the wet

and dry data sets given in Part A

Standard Error

Standard Error

• This formula is used to determine the

precision of the mean value

• You are trying to determine how confident

you are in your mean value by considering both the standard deviation and the number

• f data points

Standard Error

• How close is the calculated mean to the true

mean of the population?

Standard Error and Error Bars

• Determine the confidence in the data

collected

• 95% confidence intervals are set using + 2

SEM

• First graph the means and then add + 2 SEM

Error Bars

Error Bars DO NOT Overlap

• The data IS statistically significant, for

example:

• Claim: Sunlight inhibits leaf growth, and

therefore the width, of ivy leaves.

• Claim: Ivy leaves grow wider in shadier

conditions rather than sunny conditions

Error Bars DO Overlap

• Data IS NOT statistically significant, for

example:

• Claim: There is no statistical difference

between the average score of boys and girls

• n a test.

Standard Error

• Calculate the standard error for the wet and

dry data sets given in Part A

95% Confidence Intervals

• Random sampling of the population should

produce a mean that falls within + SEM 95% of the time