**Calculation Based: Chi-Squared Tests**

**Chi-Squared Tests Formula **

** Critical Value:** the number on the table; figure out your degrees of freedom, and ALWAYS use 0.05

- This means that you are 95% sure of it being accurate (if you pick 0.05)

** Degrees of freedom:** number of “choices” that you could possibly have minus 1

**If the chi squared value is higher than the critical value on the table, then you reject the null hypothesis. If it’s lower than the critical value, then you accept it**

**Graphs **

__Bar Graphs __

- Units: when looking at graph always figure out the units
**Margin of Errors:**

there’s a statistical difference between two sets of data *if their error bars do NOT overlap*.

When question includes margins of error, always look to see if they overlap

__Steps to Drawing Graph __

**Name the graph:**Dependent variable (y-axis) vs Independent variable (x-axis)**Label x-axis:**will be the independent variable (units!)**Label y-axis:**will be the dependent variable- If included,
**label the margins of error/standard deviation**

**Scientific Method Vocab**

**Null Hypothesis:**states that here is no statistical difference or correlation (observed diff is by chance alone)

- The null hypothesis can be rejected if test group is different from the control group
- Says that there is a similarity between two explanations or things
- Key words: resemble, like, similar

**Alternative Hypothesis**(of a test) says there is an effect/relationship

- Also says that there is another explanation; difference between two things

**Dependent Variable:**The thing you are measuring

- Changes in response to the independent variable

**Independent variable:**the thing that you are changing/testing in an experiment**Positive Control:**is not exposed to experimental treatment but is expected to have effect (Ex: positive control for movement, growth, be active)**Negative Control:**not exposed to experimental treatment or expected to have an effect

- Ex: denatured enzyme, inactive gene….

**Control:**group that does not receive the independent variable (what you are testing)

- Control group will have everything the same as experimental group, but will not receive independent variable
- So you know that any change/effect is bcuz of independent variable/thing you are testing

**Experimental Control:**

- A control can also be a benchmark which is used to determine something
- Ex: (
*thing*) is a control for (*process*)

- Ex: (
**Justify:**- “All variables must be held constant”
- Since control has not experienced the variable you are testing, any effect observed in both groups cannot be attributed to independent variable

- Know that any response/change is only bcuz of independent variable

- “All variables must be held constant”

**Environmental Factors:**vary them

- Ex: vary light, temp, duration of experiment, location
- Justify: know that any change is only because of independent variable

**TIPS ON ANSWERING QUESTIONS**

- Give short answers!! No need for long explanations
- Think in bullet points

- When asking you to compare, explicitly compare group __ with group __
- If question asks to justify including variable, probs be positive or negative control for something

Describing a trend based on a graph/table

- Point out specific parts of the graph (ie. groups with 6 mm of x had the highest rate of y)

“Identify” a certain number of things

- ONLY IDENTIFY THAT MANY! DO NOT GO OVER THE ASSIGNED NUMBER

Use specific words from the question

**CALCULATION QUESTIONS**

“Calculate total efficiency”

- If you have ___ amount of energy, but you only use ____ amount, then the amount that you actually used was the efficient part

Divide the amount that you ACTUALLY used by the amount available

**Most Missed **

- When question involves phenotypes changing, answer will probs include either directional, disruptive, or stabilizing selection
- Graph Questions:
- When describing trend, specifically point out when the line increased/decreased, and the rate it did so (rapidly or gradually)

- Explain: only need to give one answer
- Don’t need to explain the explanation; just say ___
**because**

- Don’t need to explain the explanation; just say ___

Predict: only need to predict, __no__ explanation