Bar Charts
What do the frequency counts add up to on a frequency table?
The total number of observations in the study.
What is the equation to calculate the chi square statistic?
sum of (observed-expected)^2/expected
What type of variable is chi square used to test?
Categorical
What is the process for converting an excel spreadsheet into an RStudio data file?
Download the excel file onto the computer (find it first), upload the excel file into the bottom right folder in our file (unless you have Andrea's computer), then click import into the environment on the top right as an excel file (and wait for RStudio to reformat to allow an excel conversion), then find the file and import it. Sigh...
What do the relative frequencies add up to on a relative frequency table?
100%, not the total count
What are the degrees of freedom for a chi square test?
Number of cells in the table minus 1
How do we find the null hypothesis in the original question for a chi square test?
The assumption would be all the categories would have the same values with equal distribution...unless they state a claimed distribution (for example, 70% and 30%).
What did we find out about the distribution of drinking water among those physically active and those not physically active among the 71 seniors in our survey data?
The distribution was roughly the same based on a statistical test.
When reading relative frequencies of those eating no salad, eating 1 to 3 times per week, 4 to 6 times per week, and every day, how do you find the number of people who eat at least one salad?
Add the number of people who eat 1 to 3, then 4 to 6, and then everyday together.
When comparing the chi square statistic to the critical chi square value, if your statistic is lower than the chi square value, what do you conclude?
We conclude the there is no significant difference from the expected proportions.
At the end of a chi square test, if the null hypothesis was the distribution was all equal with no preference, what can we say if we reject the null hypothesis?
We say that there is a preference for one (or more) categories, or that there is a significant difference in the expected proportions.
What biases are at play in our survey of 71 seniors?
Over-representation bias in college-level classes, instrument bias with the "bottles of water" count, and possible interviewer bias in asking about level of physical activity.
What is the difference between a bar chart and a histogram?
Bar chart is for categorical variable, bars do not touch, and are in any order. Histogram is for numerical variable, bars touch, and have values in numerical order.
Is it possible for the chi square statistic to be negative? Explain.
No, chi square is a sum of squares divided by counts, so it is impossible for chi square to be negative.
What are the three assumptions for a chi square test?
Random samples, independent observations, and all expected frequencies should be at least 5.
How many students in this class have so far told me they have been accepted to college/military/trade schools?
9 (Adonis, Maya, John, Katherine, Elias, Andrea, Rosalyn, Max, Jayden)