Kijk voordat je springt: EDA vóór hypothesetoetsen

Kleinteich en Gorb (Sci. Rep., 4, 5225, 2014) deden een interessant experiment met Zuid-Amerikaanse gehoornde kikkers. Ze hielden een plaat vast die verbonden was met een krachtsensor, samen met een lokvlieg, voor de kikker. Vervolgens maten ze de inslagkracht en de kleefkracht van de kikkertong wanneer die het doel raakte.

Kikker A is een volwassen dier en kikker B is een jong dier. De onderzoekers maten de inslagkracht van 20 slagen voor elke kikker. In de volgende oefening testen we de hypothese dat beide kikkers dezelfde verdeling van inslagkrachten hebben. Maar onthoud: eerst EDA doen! Laten we een bijenzwermplot maken van de data. De gegevens staan in een pandas DataFrame, df, waarbij kolom ID de identiteit van de kikker aangeeft en kolom impact_force de inslagkracht in Newton (N) is.

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Statistical Thinking in Python (deel 2)

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Gebruik sns.swarmplot() om een bijenzwermplot van de data te maken door de keyword-argumenten x, y en data op te geven.
Voorzie je assen van labels.
Toon de plot.

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Probeer deze oefening eens door deze voorbeeldcode in te vullen.

# Make bee swarm plot
_ = ____

# Label axes
_ = plt.____('frog')
_ = plt.____('impact force (N)')

# Show the plot
____

Code bewerken en uitvoeren

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Statistical Thinking in Python (deel 2)

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When doing statistical inference, we speak the language of probability. A probability distribution that describes your data has parameters. So, a major goal of statistical inference is to estimate the values of these parameters, which allows us to concisely and unambiguously describe our data and draw conclusions from it. In this chapter, you will learn how to find the optimal parameters, those that best describe your data.

Exercise 1: Optimal parameters Exercise 2: How often do we get no-hitters?Exercise 3: Do the data follow our story?Exercise 4: How is this parameter optimal?Exercise 5: Linear regression by least squares Exercise 6: EDA of literacy/fertility data Exercise 7: Linear regression Exercise 8: How is it optimal?Exercise 9: The importance of EDA: Anscombe's quartet Exercise 10: The importance of EDA Exercise 11: Linear regression on appropriate Anscombe data Exercise 12: Linear regression on all Anscombe data

To "pull yourself up by your bootstraps" is a classic idiom meaning that you achieve a difficult task by yourself with no help at all. In statistical inference, you want to know what would happen if you could repeat your data acquisition an infinite number of times. This task is impossible, but can we use only the data we actually have to get close to the same result as an infinitude of experiments? The answer is yes! The technique to do it is aptly called bootstrapping. This chapter will introduce you to this extraordinarily powerful tool.

Exercise 1: Generating bootstrap replicates Exercise 2: Getting the terminology down Exercise 3: Bootstrapping by hand Exercise 4: Visualizing bootstrap samples Exercise 5: Bootstrap confidence intervals Exercise 6: Generating many bootstrap replicates Exercise 7: Bootstrap replicates of the mean and the SEM Exercise 8: Confidence intervals of rainfall data Exercise 9: Bootstrap replicates of other statistics Exercise 10: Confidence interval on the rate of no-hitters Exercise 11: Pairs bootstrap Exercise 12: A function to do pairs bootstrap Exercise 13: Pairs bootstrap of literacy/fertility data Exercise 14: Plotting bootstrap regressions

You now know how to define and estimate parameters given a model. But the question remains: how reasonable is it to observe your data if a model is true? This question is addressed by hypothesis tests. They are the icing on the inference cake. After completing this chapter, you will be able to carefully construct and test hypotheses using hacker statistics.

Exercise 1: Een hypothese formuleren en simuleren Exercise 2: Een permutatiesteekproef genereren Exercise 3: Permutatiemonsters visualiseren Exercise 4: Toetsstatistieken en p-waarden Exercise 5: Toetsingsgrootheden Exercise 6: Wat is een p-waarde?Exercise 7: Permutatiereplicaten genereren Exercise 8: Kijk voordat je springt: EDA vóór hypothesetoetsen

Huidige oefening

Exercise 9: Permutatietest op kikkersdata Exercise 10: Bootstrap-toetsen voor hypothesen Exercise 11: Een bootstrap-hypothesetoets met één steekproef Exercise 12: Een tweesteeks bootstrap-hypothesetoets voor het verschil in gemiddelden

As you saw from the last chapter, hypothesis testing can be a bit tricky. You need to define the null hypothesis, figure out how to simulate it, and define clearly what it means to be "more extreme" in order to compute the p-value. Like any skill, practice makes perfect, and this chapter gives you some good practice with hypothesis tests.

Exercise 1: A/B testing Exercise 2: The vote for the Civil Rights Act in 1964 Exercise 3: What is equivalent?Exercise 4: A time-on-website analog Exercise 5: What should you have done first?Exercise 6: Test of correlation Exercise 7: Simulating a null hypothesis concerning correlation Exercise 8: Hypothesis test on Pearson correlation Exercise 9: Do neonicotinoid insecticides have unintended consequences?Exercise 10: Bootstrap hypothesis test on bee sperm counts

Every year for the past 40-plus years, Peter and Rosemary Grant have gone to the Galápagos island of Daphne Major and collected data on Darwin's finches. Using your skills in statistical inference, you will spend this chapter with their data, and witness first hand, through data, evolution in action. It's an exhilarating way to end the course!

Exercise 1: Finch beaks and the need for statistics Exercise 2: EDA of beak depths of Darwin's finches Exercise 3: ECDFs of beak depths Exercise 4: Parameter estimates of beak depths Exercise 5: Hypothesis test: Are beaks deeper in 2012?Exercise 6: Variation in beak shapes Exercise 7: EDA of beak length and depth Exercise 8: Linear regressions Exercise 9: Displaying the linear regression results Exercise 10: Beak length to depth ratio Exercise 11: How different is the ratio?Exercise 12: Calculation of heritability Exercise 13: EDA of heritability Exercise 14: Correlation of offspring and parental data Exercise 15: Pearson correlation of offspring and parental data Exercise 16: Measuring heritability Exercise 17: Is beak depth heritable at all in G. scandens?Exercise 18: Final thoughts