Fisher's exacte toets

A/B-testen in R

Lauryn Burleigh

Data Scientist

Specificaties

Niet-parametrisch, categorische data
- Of kaas- of pepperoni-pizza opnieuw wordt gegeten
Steekproef < 1000
Verwachting < 5 voor ≥ 20%
Gebruik Fisher's exacte toets voor exacte p-waarde
2x2-frequentietabel

Hypergeometrische verdeling

Waarschijnlijkheid van frequentietabel

table(Pizza$Topping, Pizza$EatAgain)

              No Yes
  Cheese     140 360
  Pepperoni   80 420

Hypothesen

Nulhypothese: geen verband tussen opnieuw eten en toppingsgroep

Foto van pizzapunten die door verschillende handen worden gepakt.

Steekproef

library(pwr)
pwr.chisq.test(w = 0.1, df = 2, 
               power = 0.80, 
               sig.level = 0.05)

     Chi squared power calculation 
              w = 0.1
              N = 963.4689
             df = 2
      sig.level = 0.05
          power = 0.8
NOTE: N is the number of observations

table(Pizza$Topping, Pizza$EatAgain)

              No Yes
  Cheese     140 360
  Pepperoni   80 420

Toets

freqtbl <- table(Pizza$Topping, 
                 Pizza$Time)
fisher.test(freqtbl)

    Fisher's Exact Test for Count Data
data:  freqtbl
p-value = 0.001809
alternative hypothesis: true odds ratio is not equal to 1
95 percent confidence interval:
 0.4569013 0.8417208
sample estimates:
odds ratio 
 0.6209987

Effectgrootte

freqtbl <- table(Pizza$Topping, 
                 Pizza$Time)
fisher.test(freqtbl)

Small: 1,5
Medium: 2,5
Large: 4
Pepperoni-pizza x 0,62 t.o.v. kaaspizza

Fisher's Exact Test for Count Data
data:  freqtbl
p-value = 0.001809
alternative hypothesis: true odds 
ratio is not equal to 1
95 percent confidence interval:
 0.4569013 0.8417208
sample estimates:
odds ratio 
 0.6209987

Power

library(pwr)
pwr.2p.test(h = 0.62, n = 500, 
            sig.level = 0.002)

    Difference of proportion power 
 calculation for binomial distribution

              h = 0.62
              n = 500
      sig.level = 0.002
          power = 1
    alternative = two.sided

NOTE: same sample sizes

Laten we oefenen!

A/B-testen in R