Questions tagged [qq-plot]
A qq plot (or quantile quantile plot) is a scatterplot of the quantiles of two distributions. QQ plots are useful for comparing distributions.
323
questions
3
votes
1
answer
651
views
I have applied many statistical tests to my data, but still cannot determine normality
I have run multiple tests to determine normality on my dataset, but I am unsure which one to adhere to, especially since my histograms, density plots, and QQ plots leave much to be desired in terms of ...
- 53
0
votes
0
answers
24
views
How to interpret a qq plot of uniform distribution whose slope is greater than 1
I am trying to interpret a qq plot of a uniform distribution in R where the plot is as shown in the image. The qq lines are a kind of straight but the slope of these lines way greater than the 45 ...
0
votes
0
answers
27
views
Distribution looks roughly normal on a q-q plot, but has a p-value of 0.0 for the Shapiro-Wilk normality test. How to interpret? [duplicate]
The distribution is as follows:
However the Shapiro-Wilk test yields a p-value of 0.0 and a W statistic of 0.9. There are over 7,000 values in the sample.
Note, the quantile values have been ...
- 111
2
votes
1
answer
161
views
Trouble selecting q-q plot settings with statsmodels. Do any of these plots properly compare the sample quantiles to theoretical normal quantiles?
I have an array of over 6,000 data points and am trying to show whether they follow a normal distribution. Statsmodels (the library I'm using to generate plots) gives the option of using a 45-degree ...
- 21
0
votes
0
answers
18
views
Does the maximum likelihood estimate give the optimal line of fit in a QQ plot?
Many analysts attempt to fit a distribution for a random variable by a. estimating the parameters with maximum likelihood then b. assessing the quality of the fit to the distribution by inspecting a ...
- 59.4k
2
votes
2
answers
95
views
Distribution and variable analysis
I am doing a statistical test (program used is SPSS). On the basis of distribution and sample size, I have to chose the correct variable analysis. I also have to justify every decision. I have two ...
- 21
0
votes
0
answers
49
views
Does this need to be transformed? If, yes, how?
My data is collecting deposition of particles from the atmosphere once a month for 11 months at two sites. I am testing to see if my two sites' data are normally distributed so I can determine what T-...
- 1
3
votes
1
answer
165
views
Help me understand this qqplot
I have plotted the qqplot of the residuals that my model generates with
the python module statsmodel
sm.qqplot(data, line ='r') and it looks like this
The points are placed on a straight line but ...
- 325
0
votes
0
answers
30
views
How do I interpret this QQ plot?
I am calculating a multiple regression with a sample of 128 and I was wondering, what distribution would best describe this residuals qq plot? It seems like a a Poisson-distribution to me, is it ...
- 1
1
vote
0
answers
37
views
Q-Q plots and normality: Can I use ANOVA?
I want to use an ANOVA for my analysis (2x3 design). I can decide if I can safely use parametric tests. The two samples results: Shapiro-Wilk p<.001) and Q-Q plots don't seem to be normally ...
3
votes
1
answer
120
views
Evaluating goodness-of-fit for GARCH models in R with QQ-plots (rugarch package)
I'm currently working with multivariate GARCH representations of time-series for financial data using the rmgarch R package. This package in turn uses the well-...
- 31
2
votes
1
answer
978
views
How to define the line to fit in Q-Q plot?
I'm trying to figure out if my data follows a normal distribution and if it contains outliers. I have plotted the histogram and now I would like to plot the quantile-quantile (Q-Q) plot. My point is, ...
- 123
0
votes
0
answers
173
views
Drawing Q-Q plot with ggplot2 and interpreting it
I'm learning how to draw Q-Q plots using R from Modern Statistics with R
. The codes below compare the msleep$sleep_total data with a normal, lognormal, and a ...
- 409
0
votes
0
answers
26
views
SDR vs fitted value plots interpretation of using quasi-poisson and poisson
can someone help me to illustrate the following question based on the posted plots:
Q1: generally speaking, we want the SDR follows a normal distribution with mean 0 and a constant variance. In the ...
0
votes
1
answer
52
views
Goodness-of-fit Tests
Continuing from my previous question here.
Furthermore, I intend to perform the chi-squared test and plot QQ-plots to test the hypothesis $H_0:\lambda=1$. I do not get to see the actual data though; I ...
- 107
4
votes
1
answer
192
views
Goodness-of-fit Tests
I wish to test whether a large number of observations $X_i$ follows an exponential distribution with parameter $\lambda=1$. I also wish to test this hypothesis exactly, and intend that if the ...
- 107
0
votes
0
answers
550
views
Different Calculation Methods for Theoretical Quantiles of Q-Q Plot
There seem to be at least two different methods to calculate the theoretical quantiles in a Q-Q plot. In the following, the normal distribution is assumed to be the theoretical distribution.
Split ...
- 35
0
votes
1
answer
45
views
How can the author get the following conclusion from the QQ plot?
In this paper: https://www.tandfonline.com/doi/pdf/10.1080/02664763.2021.1940109, the authors have two actual datasets (e.g., 59 observations showing continuous annual flood data) and the authors want ...
- 647
0
votes
0
answers
61
views
Frequentists tests to check for normality
Let $X_1,...,X_n\sim X$ be $n$ i.i.d. random variables. I want to to test if they follow a normal distribution, in other words, check if their distribution belongs to the Gaussian family.
These are ...
- 107
1
vote
1
answer
250
views
Interpreting QQ plot
Can we say that the assumption for linearity is met? I'm confused because the tails are heavy, and deviations have a bow-shaped pattern. Still, I think that the linearity has met because the majority ...
- 11
1
vote
1
answer
112
views
Interpreting 2 residuals plots [closed]
Hello. Can anyone help me with interpreting these plots? I would like to know what assumptions of the linear model are not being met and what method should be used to fix the problems. I think there ...
- 11
1
vote
0
answers
1k
views
How to choose between ordered logit and ordered probit regression?
If the dependent variable is discrete ordinal, like 0-10 then an ordered logit or ordered probit is appropriate to use. They are both similar but their interpretation are different and their error is ...
- 65
0
votes
1
answer
50
views
Can we compare a standardized version of a variable with a standard normal distribution to check a variable's normality?
I am currently exploring ways to check the normality of a given variable in the dataset. Since most algorithms assume a variable's gaussian distribution, it is important to check it.
A Q-Q Plot
Came ...
- 123
2
votes
1
answer
80
views
Is there normality in my data? Which statistical test should I use?
I runned two GLMs using the same dependent and independent variables, but modelling each analysis according a different type of distribution. Then, I compared its AIC values to find what distribution ...
user351644
0
votes
1
answer
94
views
Does this plot indicate the data is normal distributed?
I use qqnorm to plot my data as the photo attached. Does this plot indicate the data is normal distributed?
- 11
0
votes
1
answer
22
views
Checking interaction between one dependent continuous variable and two independent continuous variable
I am trying to figure out if there is a way that we can perform some statistical test to check the interaction between two independent continuous variables and a dependent variable in R.
I have three ...
0
votes
0
answers
42
views
How do I interpret this plot?
I'm finding it hard to interpret this plot. Is it skewed, bimodal, or what is it? What do the points lying in the same line and rising suddenly mean? Is it exponential?
0
votes
0
answers
59
views
Theoretical q-q plot: What does the f-value mean in this example?
I am looking at this article on theoretical q-q plots and am trying to understand it in its entirety. The part where I get lost is when the author writes:
We first find the f-values for alto
What do ...
- 43
0
votes
1
answer
2k
views
What are the main difference between a QQ plot and a probability plot for measuring nomality? [duplicate]
I am trying to evaluate the normality of the distribution of my model's residuals.
I have been using statsmodels.api.qqplot and ...
- 205
2
votes
1
answer
289
views
Is my data normally distributed? (QQ plot and histogram analysis) [duplicate]
I am trying to create a regression model for prediction. I need to generate prediction/confidence intervals for my model.
I am trying to decide whether to use a quantile regression or linear ...
- 205
3
votes
1
answer
449
views
Calculation of quantiles with fitted parameters in Python
I am trying to make two-sample Q-Q plots in Python.
A Python function that is used for calculating quantiles has the option of fitting parameters for the calculation of quantiles. These parameters are ...
- 75
4
votes
1
answer
222
views
Is it possible to make a confidence envelope for a two sample Q-Q plot in R (or Python)? If so, what is the simplest method?
I want to show the confidence envelope for a two sample Q-Q plot in R (or Python). The aim is to use the Q-Q plot to give an indication of whether my two samples are drawn from the same population
The ...
- 75
1
vote
2
answers
826
views
Quantile-Quantile Plot for Negative Binomial Distribution
I am performing regression analysis in R on count data which are negative binomial distributed. I would like to use a quantile-quantile plot as a tool to diagnose the fit of my models, but I am ...
- 11
4
votes
2
answers
261
views
GAM: Find a good distribution for the monthly data sums?
I am new in the GAM modelling. I would like to find a family, that will fit my response variables. I am using the sums of monthly counts of beetles, collected from the beetle traps in ~ two weeks ...
- 263
0
votes
1
answer
129
views
Which statistical test do I use with 2 independent groups and 1 dependent variable
I want to test if there is a difference in the mean distance travelled (Afstand) by sex (Geslacht) and age class (...
- 103
0
votes
1
answer
70
views
QQ Plot interpretation
I wanted to investigate if my data is normally distributed with a QQ Plot. I'm not quite sure if the deviations from the theoretical plot are too big to crate a bland-altman plot?
- 31
10
votes
4
answers
4k
views
Why is my data not normally distributed while I have an almost perfect QQ plot and histogram?
I am doing a thesis and I am stuck with my statistics on time series data. And when I run a Shapiro test, or any test, it says:
...
- 103
0
votes
1
answer
296
views
Quantile-quantile plot from scratch and comparing to multiple standard distributions
I want to do a QQ plot, where I compare a sample to multiple standard distributions, scaled, so that the points represented by the correct distribution are on the black line.
I expect to do basically ...
- 545
2
votes
2
answers
704
views
QQ plot result doesn't correspond to normality test [duplicate]
I am considering an ANOVA model for such data:
...
- 27
0
votes
0
answers
33
views
How to interpret a point in the qq plot? [duplicate]
I am trying to understand the Q–Q plot.
Suppose I create a sample according a exponential distribution
...
- 264
2
votes
1
answer
857
views
What is y-axis on QQ plot?
I have a simple question about QQ plots in simple linear regression, but I am a bit confused about the plot: depending where i look the y axis is different: it can be either 1) residuals 2) ...
- 293
2
votes
1
answer
232
views
Random Effect in twin study of both MZ and DZ twin pairs
I am a bit stuck with the use of linear mixed models and its random effects in a twin study analysis. What I have is microbiome data for twins that are from MZ twin pairs and DZ twin pairs, so no ...
- 21
1
vote
1
answer
207
views
qqplot result and normality for ANOVA
The independent variable is promotion, and it is assigned to 3 groups. The dependent variable is sales revenue. I have 172 observations of sales revenue for promotion group 1, 188 for group 2 and 188 ...
- 53
2
votes
0
answers
198
views
Interpret the QQ plot of multilevel logistic regression
I'm doing multilevel logistic model in R. To check the model diagnostic, I draw the following QQ plot. But it seems hard to say in which way it skews. I'm a bit confused what conclusion can we draw ...
- 41
0
votes
1
answer
930
views
Dealing with bimodal residuals
I want to run linear models to understand the effect of single predictors on an outcome. This is quite straightforward, but I am facing a situation where my residuals appear to be bimodal.
I can't ...
- 45
0
votes
1
answer
210
views
How to use R to plot $f_n(\theta)$ based on following samples? [closed]
For iid random samples $X_1,\dots, X_n$ with mean value $E X_1=\theta$, take $X_{(1)}=\min \{X_1,\dots, X_n\}$ and $X_{(n)}=\max \{X_1,\dots, X_n\}$. If $\lambda$ solves equation
$$
\sum_{i=1}^n \frac{...
- 647
4
votes
1
answer
1k
views
How to interpret this qqplot?
I wonder how to interpret this plot. I know, in general, that a qqplot depicts the quantiles of the data against the quantiles of the normal function.
How do I apply this to this plot?
- 3,123
0
votes
0
answers
692
views
Equally spaced points on x-axis in exponential distribution probplot/qqplot
I have a sample distribution and want to check if it is exponential. For that I am trying a qqplot and probplot.
...
- 213
3
votes
1
answer
1k
views
Quantiles from histogram?
Is it possible to calculate quantiles from a probability histogram P(x) rather than from the data x itself? I have an unbinned histogram for discrete random variables, and I'm wondering if I can ...
- 213
0
votes
1
answer
49
views
Finding the region in sample data that fits to a known distribution
Given sample data that have a known probability distribution for large x and an unknown probability distribution for small x, what is the best way to find the value of x where the known probability ...
- 213