Experimental Design AP Biology Test

define independent variable

“you are changing” variable is manipulated or changed by the researcher. variable will vary between experimental groups

purpose of experimental design

to plan effective experiments that utilize the scientific method

describe a foundation of good science

an observation and testable question

steps of the scientific method

ask a question, background research, construct a hypothesis, test with experiment, analyze data and construct a conclusion

required parts of an experiment

hypothesis, independent variable, dependent variable, and constant variable

alternative hypothesis?

“If, then” statement

educated prediction about the results of the experiment

null hypothesis?

states that the independent variable has no affect on the dependent variable. A statistical hypothesis, assumed to be correct unless proven otherwise by data

main difference between a null hypothesis and an alternative hypothesis?

Null hypothesis does not affect the dependent variable, while the alternative hypothesis does.

define a dependent variable

“what is being measured” variable changes in response to the independent variable

define constant variable

variables that remain the same in every group of an experiment. essential to ensure that the changes in the DV are being caused by the manipulation of the IV

out of light intensity and plant growth, what is the IV?

light intensity

out of light intensity and plant growth, what is the DV?

plant growth- dependent on the light to grow bigger

out of light intensity and plant growth, what are a couple constant variables?

water, the same plant, the pot, soil

describe a positive control group

group that receives “normal” amount/ type of the independent variable

describe a negative control group

group that does NOT receive the IV at all

describe an experimental group

group that receives various amounts/types of the IV, that is DIFFERENT than the control group.

define the term sample size

all of the data points together/ number of individual items tested in an experiment

explain the relationship between the sample and statistical analysis.

the bigger the sample size= the better statistical analysis. the better statistical analysis= better support of the conclusion

what axis is the dependent variable labeled

Y

what axis is the independent variable labeled

X

what needs to be included when you label the axes

label the units

when should you use a bar graph?

when the IV is sorted into experimental groups or categories

when should you use a line graph?

when calculating the rate (rise/run) or wanting to find the overall trend

what is the purpose of a graph title

to describe what the graph is showing without giving information about the conclusions

Do you have to have a graph title on the AP test?

No

what are the parameters for scaling the graph

include all of the data points and should take up the entire area of the graph

what is the equation for scaling an axis

highest number/ the number of squares on axis

list the 4 steps for analyzing the graph using CER (Claim, Evidence, Reasoning)

1- identify the scientific question

2-make a claim

3- find evidence to support the claim

4-find reasoning that explains the relationship between the claim and the evidence.

purpose of calculating the mean?

tells you the “normal” or average of the collected data

what is the formula to find the mean?

sum of points collected/ # of points

difference between true means and sample means

the true means captured the means from every member, while sample means averages within individual experimental groups

what is the purpose of standard deviation as a statistical test

Quantifies the amount of variation in a data set; allows for comparison data within a sample to see if a certain point is statistical different than the average

purpose of standard ERROR of the mean test

to see the probability of capturing the true mean

what is better, a bigger or smaller SEM?

The smaller SEM= the more likely the sample mean matches the true mean

how to calculate +/-2 SEM, top and bottom?

top mean +2SEM; bottom mean -2SEM

what does it mean if the error bars overlap between 2 groups

if they overlap, then the differences in the sample means are NOT statistically significant, possible for true means to be the same

what does it mean if the error bars DO NOT overlap between 2 groups

differences in the samples means ARE statistically significant, leaving less than a 95% chance that the true means are the same for both groups

what is normalcy and why is it important?

normalcy within a data set is determined by calculating the mean, median, mode, range, and standard deviation of a sample. comparison of data points, confirmation of trends or patterns in the data and statistical analysis can only occur after establishing normalcy.