Lecture 7 - Comparing Groups I
# Topics for today! 1. Topic: table(), 2. Topic: chi.sq() 3. Topic: binom.test() 4. Topic: prop.test() ## Data ```{r} setwd("~/Desktop/R Materials/mih140/Lecture 5 - Introduction to Plotting in R") flight_data = read.table("RegionEx_Data.txt", header = T, sep = "\t") # load in flight_data ``` ## 1. Topic: Tables ```{r} # Example: Count how many observations are from MDA flights airlines = flight_data$Airline # vector of airlines num_mda_flights = sum(airlines == "MDA") # counts how many flights are MDA # Alternative way: Using table(). The table function takes in a vector of catagorical data i.e.: tab_airlines = table(airlines) tab_airlines / sum(tab_airlines) # table of frequencies instead of count. # table() can take in multiple vectors of catagorical data tab_airline_airport = table(flight_data$Airline, flight_data$Origin.airport) # table() also understands columns of a dataframe table(flight_data[,c("Airline", "Origin.airport")]) ``` ## Tables cont. ```{r} # QU: Lets see if flights are uniformly distributed through out the week. days = table(flight_data$Day.of.Week) chisq.test(days) days_airlines = table(flight_data$Day.of.Week, flight_data$Airline) res = chisq.test(flight_data$Day.of.Week, flight_data$Airline) ``` ## 2. Topic: Chi-squared test ```{r} # QU: Is day.of.week and whether or not the flight is delayed independent? tab = table(flight_data$Day.of.Week, flight_data$Delay.indicator) chisq.test(tab) ``` ## Chi-squared test cont. ```{r} # QU: Is airline and whether or not the flight is delayed independent? tab = table(flight_data$Airline, flight_data$Delay.indicator) results = chisq.test(tab) results$observed results$expected ``` # 3. Topic: binom.test(). ```{r} # Syntax for binom.test(): ## binom.test(successes, N, p, alternative = , conf.level ) # QU: Is the proportion of delays statistically signifigantly different than .2? delays = table(flight_data$Delay.indicator) binom.test(delays) # default with p = .5 binom.test(delays[2],sum(delays),p=.2, alternative = "two.sided") # Correct test ``` # 4. Topic: prop.test(). ```{r} # Syntax is the same as binom. delays = table(flight_data$Airline, flight_data$Delay.indicator) prop.test(delays) delays = table(flight_data$Delay.indicator) prop.test(delays) # default with p = .5 res = prop.test(delays, alternative = "two.sided", conf.level = .95) # Correct test ```
