Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

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.

0
votes
1answer
21 views

Interpreting qq plot from ARIMA residuals

Im trying to undestand this qqplot from arima residuals but im a bit lost about the underlying distribution, concretely I don't now how to interpret the tails.
0
votes
0answers
19 views

If there are covariant variables in the exponential distribution, how do I draw the QQ plot?

Observation Data X=x[1],... x[n]; covariant variables are eta=eta[1],...,eta[n]. The parameters of exponential distribution are composed of covariant variables(eta) and lambda. So, X[i]<-rexp(eta[i]...
0
votes
0answers
16 views

Confused about the statistical tests to choose or any transformation to apply

I am new to the stackexchange, so please forgive me for my editing ignorance. I am confused and stuck about how to proceed further with my data. I have the following data ...
0
votes
0answers
19 views

Is Linear regression good to such Q-Q plots

I am beginner to Machine Learning. So, I was looking at the Q-Q plot of underlying data on which i was thinking to apply linear regression. Could you please suggest below is my Q-Q plot. Whether is it ...
0
votes
3answers
234 views

Ways of visually comparing variance of data [closed]

I have a dataset containing 8 categories, I now want to visually compare the variance between the categories. The most common approach would be to use box plots or violin plots but I would like to ...
0
votes
1answer
41 views

An explanation of the choice of QQ-line in a normal QQ-plot

The standard precedure for making a QQ-line in a normal quantile-plot is to draw a line through the first and third sample quantile. My question is why? If data follows a normal distribution, then ...
0
votes
1answer
22 views

Approximating location and scale from QQ-plot

So I'm solving old exams in preparation for my statistical data analysis exam and came by this question. "b) Using the QQ-plot of the location-scale family that you have selected under part a, ...
0
votes
0answers
41 views

Testing normality with Confidence Intervals

I've read an article that talks about transforming non-normal data to normal data. In the article it says: "In this case, normality clearly cannot be assumed; the p-value is less than 0.05 and more ...
1
vote
0answers
29 views

Why don't my GWAS QQPlots look the same?

I am trying to create a QQPlot of 100 log-transformed p values from a GWAS study. The idea is that taking the -log(p) will magnify the smallest p values to make them easier to see. (reference) I was ...
0
votes
0answers
24 views

How to verify assumptions of a normal distribution? [duplicate]

I'm working with the iris data.I made a density plot And a qq plot For sepal Length.It looks Approximately normal With the left skew And a flat peak The points In the qq Plot Stay within The ...
0
votes
0answers
12 views

Reference line for QQPlots: robust regression vs quartiles method

Using the car package, I drew two qqPlots of 144 p values from correlated tests on one dataset. The top plot uses a reference line drawn by "quartiles" and the bottom plot uses a line drawn by "robust"...
2
votes
1answer
231 views

Interpreting Regression Diagnostic Plots

I'm sorry if this is a broad question but can someone explain to me how to interpret these regression diagnostic plots? I understand the Normal Q-Q show's how normal the spread of the data is, but the ...
4
votes
1answer
59 views

Introducing random slopes in nested model improves model fit but residuals variances become unequal

I have measured boldness scores (continuous variable) across time (trials) for individuals (ID) within colonies (colony). The data is coded such that individuals 1-30 belong to one colony, 31-60 to ...
2
votes
1answer
212 views

Interpreting a “wavy” QQ plot?

I am observing the following QQ plot produced from an OLS linear regression fit of my data: Many other SE questions discussion QQ plot interpretation, but this is an extremely regular (but non-...
3
votes
2answers
107 views

When checking for normality, would you prefer numerical methods or graphical methods?

I would like to know what is your preferred way to decide when the deviation from the normal distribution is relevant. when saying "relevant", I not saying necessarily "statistically significant". ...
3
votes
2answers
175 views

Strange qqplot for poisson gam

I've built a gam using mgcv and the following code ...
1
vote
3answers
91 views

How long is a distribution considered normal?

I have a dataset of metric distances ($n=5800$) and plotted those as a histogram. My initial thought was that this distribution looks normal. But after performing a Shapiro Wilk test and plotting the ...
0
votes
1answer
61 views

Non-parametric tests for interaction effects

I have two datasets that are both organised as follows: an algorithm calculated a quality score (Q) of a specific image (image) that was processed using a certain algorithm (method). One has 315 ...
0
votes
0answers
118 views

Assuming heteroscedasticity produces terrible QQ plot

I created a model using the lm function and obtained a model with an AIC of 390516.1 and the following QQ-plot: However, the Breusch-Pagan Test returned a p-value ...
1
vote
0answers
64 views

Granularity in a Normal Quantile Plot

I'm having some trouble understanding the concept of granularity so I'd like to have some clarity in this regard. After producing a normal Q-Q plot of some data (seen below), a question has asked me ...
2
votes
2answers
152 views

Q-Q plot, is this a approx normal distribution?

I searched online and looked video tutorials but I'm still not sure. Would you consider the below data normally distributed? I know the ideal fit in theory would be that most of the points are on the ...
1
vote
1answer
338 views

Need help interpreting a chi-square Q-Q plot for multivariate normality

I would like to know if my interpretation is correct with respect to the Q-Q plot I made (see the first image below). The second image is a plot of a chi-square distribution. At the first half, it ...
1
vote
1answer
72 views

Remove points from QQ plot of genome-wide association study

I have results from a genome-wide association study, which is basically a bunch of univariate tests (akin to linear regression). Results include statistical significance of each test, and thus I want ...
1
vote
1answer
45 views

What can we do given percentile values of the data? [closed]

We are given 20 percentile values say equally spaced percentiles 0 to 100 and also the sample size. Basic things we could do is figure out if this is normal using qq plot, other than that what else ...
1
vote
1answer
104 views

Is this QQ convex or concave?

With my data I got this exponential QQplot : is this QQplot convex or concave ? Thanks in advance
1
vote
1answer
148 views

A question about qqplot

This is my qq plot : Its concave-convex curve so it indicates light tails. But my mean excess plot : is increases which means the tail of the distribution of my data is heavy-tailed. I don't ...
1
vote
1answer
1k views

How to create a QQ plot compared to a function I define?

I want to create a QQ plot with my sample data compared to the PDF $e^{-y}$. My $y > 0$. My first approach was to create a random vector of values > 0, then plug those into $e^{-y}$ to get the ...
6
votes
2answers
2k views

QQ plot and $x = y$ line

If my qqplot is linear but the gradient is not the same as the 45 degrees line, what does this suggest? I am trying to examine the fit of laplace distribution to my sample data, so I randomly ...
0
votes
1answer
282 views

Fat Tails and Volatility clustering relationship

Let's say I have a return time series that after a proper ARMA modelling exhibits fat-tallness from QQ-plot. Can this be a consequence of volatility clustering so that by applying a GARCH model I ...
0
votes
0answers
34 views

Q-Qplot with outliers on the same side?

What does it mean when there are outliers in a Q-Q plot on the same side of the plot at both ends of the tails? I've attached the example I have, which is showing the residuals for the abundance of my ...
2
votes
0answers
112 views

Mismatch between KS test and qq plot?

I read many posts about the Kolmogorov-Smirnov test, Q-Q plots and CDFs. I decided to ask my own question about some difficulties I have with some real data. The data I'm using is available on this ...
0
votes
0answers
194 views

What is the algorithm for computing quantiles? [duplicate]

According to the Matlab documentation for qqplot, the ith ordered value is plotted against the ...
0
votes
0answers
53 views

What is a qq plot? Is it possible to make a qq plot between age (ranging from 20 to 70) and salary (ranging from 5000 to 10000)?

What I have understood is that it is a graphical technique used to check if 2 data sources (even if not from the same population) have similar data distribution. In that case the scatter plot will be ...
0
votes
1answer
70 views

Correct approach to carry out Q-Q Normal plot in R?

I am attempting to test some sets of data for normality. I have 64 groups to test. Each group has n=8 samples. [[I am aware of the problems with low n in regard to normality testing]] My end goal is ...
0
votes
0answers
93 views

Advice on negatively skewed residuals

I am running a simple one-way ANOVA of a continuous dependent variable and my two-level categorical independent variable. n value = 408; 198 in my control condition and 210 in my experimental ...
0
votes
2answers
247 views

Transform variables so residuals become normally distributed

I'm doing a project which involves multiple regression, and I'm aware (as far as I understand) that the residuals should be normally distributed with a constant variance. From my study, the residuals ...
1
vote
0answers
36 views

Does taking Ln of dependent variable improve assumptions of a multiple regression?

I have run two multiple regressions in R, one with average abundance as dependent variable, and one with log avg abundance as dependent variable. With the given plots, can we say one of the two ...
0
votes
1answer
460 views

What are the 'critical' values of skewness and kurtosis for normality assumption? [duplicate]

I am analyzing buy-and-hold abnormal returns of stocks (dependent variable) using OLS regression. These returns, however, tend to be positively skewed (and are so in my case). The residuals obtained ...
2
votes
2answers
162 views

Groups of Points in QQ Plots

While using QQ Plots, I always notice these 'groups' of points; many sets of points arranged in a straight line and sometimes in a curve as shown below: exponential: normal: The theoretical ...
-1
votes
2answers
1k views

Identifying the normality by QQ plot

I have three variables and I want to know which of them can be considered to have the normal distribution. Variable A Variable B Variable C
3
votes
2answers
1k views

How to interpret negative quantiles on a qqplot?

I am having troubles interpreting the qq plot below. The histogram is residuals from linear regression. How to interpret negative theoretical and sample quantiles? Shouldn't it be [0,1]?
1
vote
0answers
135 views

Making a qqplot in R for functions

The question is: given that I have a data set and a theoretical cumulative distribution defined as a function, how can I make a qqplot to compare them? I cooked up a solution as follows: I chose a ...
1
vote
1answer
181 views

Is the assumption of constant variance violated in the following?

Is the assumption of constant variance violated in the following? I am measuring point in a 3D coordinate system (X,Y,Z) using 10 different methods. One method is the golden standard (reference). The ...
3
votes
0answers
218 views

Convention of QQ Plot Axes/ Axis Labels

I am building qq plots with a statistics package, however I notice my output is different than what I found in the econometric literature. For example, here is a qq plot from a publication I came ...
1
vote
2answers
116 views

Checking assumption of normality with multiple subsets of unequal size

I have a dataset consisting of 12 subsets, each subset contains between 10 and 15 temperature observations from one person. I would like to determine whether or not it is reasonable to assume ...
1
vote
0answers
174 views

Question regarding qq plot of transformed data; what's the right transformation to use

So I will post qq of original data first along with logarthmic transformed data. If I'm interpreting the first correctly it looks like there is right skew to the data. The log transformed has a 'bulge'...
4
votes
1answer
1k views

Why residual plots are used for diagnostic of glm

I asked this question here which @Glen_b had kindly answered. I thought I could get a more detailed explanation with references if I posted it as a whole new question. So my questions is why ...
1
vote
1answer
3k views

residual vs. QQ-plot in multiple regression

I'm working on a Kaggle multiple regression tutorial competition and inspecting plots of my residuals. I followed a suggestion and log transformed several independent variables and the dependent ...
0
votes
1answer
444 views

QQ-plot doesn't correspond with histogram

I made a histogram and QQ-plot, using this code: ...
1
vote
0answers
21 views

Mix Design: Failure to predict response

I have performed a mixture design containing 3 terms and I have carried out 6 experiments needed to adjust a quadratic model. It fitted the data quite well: ...