AP Bio Unit 0

controlled experiment

controlled experiment

scientific test done under controlled conditions (one or a few factors changed, all others constant

has independent variable, dependent variable, control groups, experimental groups, and constants (controls)

before the experiment

observation, scientific question, hypothesis, controlled experiment developed, research (typically)

independent variable

experimenter controls and changes across groups

ex) changes in water temperature for goldfish

dependent variable

changes in response to other variable

ex) change in respiration rate for goldfish

constants/controls

identical other variables across all groups

ex) goldfish species, size, tanks

experimental groups

receives some independent variable

control groups

no independent variable, baseline to see if IV has an effect

negative control groups

no additional treatment, identical to experimental groups just without the independent variable

positive control group

includes additional treatment that is known to cause the effect, identical to control groups except they have additional treatment and no independent variable

tests to see if the setup is working right

hypothesis

strong if it has a dependent variable, independent variable, is testable, and makes a specific prediction

“if-then”

bar graph

used for categorical groups

histogram

distribution of outcomes

count the occurrence of outcomes in divided ranges for continuous variables

one axis ranges, one axis frequences

BARS DO TOUCH

continuous variables

not discrete/categorical values, but along a spectrum

ex) temperature, time (usually), test scores

box and whisker plots

summarized data distribution

uses a “five number summary”

arrange smallest to largest, find minimum and maximum, median (middle number), lower quartile (left median), and upper quartile (right median)

scatter plots

overall relationship between two continuous variables

independent variable x-axis, dependent variable y-axis

draw line of best fit through average/middle of all points

line graphs

track changes over time between two continuous variables

x-axis usually time

chosen over scatter plots whenever individual changes from point to point need to be seen

pie charts

compare categorical groups proportionally (fraction or percentage of total)

graphs

have title, labeled axes with units if possible, scaled x and y axes

standard error of the mean

higher = more inaccurate, lots of deviation/variation

lower = less inaccurate, less deviation/variation

±2 of this to construct error bars (95% certainty not to chance)

chi squared test

1) null hypothesis (consistent with expected) and alternative hypothesis (doesn’t match expected

2) find expected counts

3) chi-squared value = sum of (o-e)²/2

4) degrees of freedom = possible outcomes - 1; p-value of 0.05 on chart

5) chi-squared less than critical value = NOT STATISTICALLY SIGNIFICANT

if chi-squared is greater than critical value, it is statistically significant (do not accept null).