Unit 0: Experimental Design Topics 1-2

controlled experiment

controlled experiment

only one or a few factors changed

independent variable, dependent variable, control groups, experimental groups, constants

5 components of controlled experiment

observation, scientific question, hypothesis, controlled experiment, research

5 things done before an experiment

independent variable

experimenter controls and changes between groups (eg changes in water temperature)

dependent variable

predicted to change in response (eg changes in respiration rate)

constants/controls

kept identical across all groups, dependent variable not affected (eg fish size, species, tanks)

experimental groups

groups that receive independent variable, can be more than one

control groups

baseline to see if independent variable works, can have more than one or none

negative control groups

NO additional treatment, identical to experimental but with no independent variable (eg the original tank)

positive control groups

receive additional treatment known to produce expected effects and nothing else is causing it to not change (eg caffeine in the water)

testable, independent and dependent variables, specific prediction

strong hypothesis (can use “if-then”)

data tables

record and organize experimental data

graphs

patterns or trends between variables

bar graphs

data for categorical groups

categories on axis, measured value other

BARS DO NOT TOUCH

histogram

distribution of outcomes

number of outcomes in divided ranges for continuous variables (spectrum)

one axis has range, other has frequency

BARS TOUCH

continuous variables

not discrete but exist along a spectrum (eg scores, temperature, height, time, etc)

box and whisker plots

more summarized distribution of data, comparable

“five number summary” = max value, min value, Q1, median, Q3

arrange smallest to largest

scatter plots

overall relationship between two variables

both axes have a continuous variable

INDEPENDENT VARIABLE ON X AXIS, DEPENDENT ON Y

line of best fit

line of best fit

average of points, about the same above and below

linear in AP Bio

dotted line past points

line graphs

relationship between two continuous variables from point to point (like time), not trends

X AXIS usually TIME, y axis usually variable

pie charts

compare categorical groups proportionally

data either a fraction or percentage

descriptive title, labeled axes with units, scaled x and y axes

3 steps how to construct a graph (not including scatter plot for line of best fit)