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3 Parameter item characteristic curve from Item response theory (IRT), written with python
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from scipy.stats import norm | |
import numpy as np | |
import matplotlib.pyplot as plt | |
a, b, c = 1, 0, 0 | |
D = 1.702 | |
def normal_ogive(theta, a=1, b=0, c=0): | |
return c + (1 - c) * norm.cdf(a*(theta - b)) | |
def logistic(theta, a=1, b=0, c=0, D=1.702): | |
return c + (1 - c) / (1+np.exp(-D *a * (theta - b))) | |
def plot_params(a=1, b=0, c=0, D=1.702): | |
thetas = np.linspace(-3, 3) | |
title = f'Discrimination(a)={a}, Diff(b)={b}, Guess(c)={c}, Scaling(D)={D}' | |
plt.figure(figsize=(8, 6)) | |
plt.title(title) | |
plt.plot(thetas, normal_ogive(thetas, a, b, c), label='Normal Ogive') | |
plt.plot(thetas, logistic(thetas, a, b, c, D), label='Logistic') | |
plt.legend(prop={'size': 13}) | |
plt.grid() | |
plt.show() | |
plot_params() |
Author
1pha
commented
Feb 1, 2021
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