I have one sample and several features.  I calculate a z-score for various features, and for various combinations of features.  Is there a way to quantify the significance of the difference between two z-scores?  For example, suppose I calculate a z-score for the combination of features (male, homeowner) and also for the combination (male, homeowner, married).  For one scenario, suppose the first z-score is 3.0, and the second z-score is 6.0.  For a different scenario, suppose the first z-score is 25.000, and the second z-score is 25.001.  I'm trying to determine whether or not (male, homeowner, married) is a better predictor than (male, homeowner).  Is there a generally applicable formula to quantify the significance of the difference, perhaps taking into account the sample size?  I have no training in statistics, and am trying to implement a software program.  A cookbook formula accompanied by some beginner-appropriate explanation would be ideal and greatly appreciated.  Thanks
This seems to be a basic issue, but I just realized that I actually don't know how to test equality of coefficients from two different regressions. Can anyone shed some light on this?   More formally, suppose I ran the following two regressions:  $$ y_1 = X_1\beta_1 + \epsilon_1 $$ and  $$ y_2 = X_2\beta_2 + \epsilon_2 $$ where $X_i$ refers to the design matrix of regression $i$, and $\beta_i$ to the vector of coefficients in regression $i$. Note that $X_1$ and $X_2$ are potentially very different, with different dimensions etc. I am interested in for instance whether or not $\hat\beta_{11} \neq \hat\beta_{21}$.   If these came from the same regression, this would be trivial. But since they come from different ones, I am not quite sure how to do it. Does anyone have an idea or can give me some pointers?   My problem in detail: My first intuition was to look at the confidence intervals, and if they overlap, then I would say they are essentially the same. This procedure does not come with the correct size of the test, though (i.e. each individual confidence interval has $\alpha=0.05$, say, but looking at them jointly will not have the same probability). My "second" intuition was to conduct a normal t-test. That is, take   $$ \frac{\beta_{11}-\beta_{21}}{sd(\beta_{11})} $$  where $\beta_{21}$ is taken as the value of my null hypothesis. This does not take into account the estimation uncertainty of $\beta_{21}$, though, and the answer may depend on the order of the regressions (which one I call 1 and 2).   My third idea was to do it as in a standard test for equality of two coefficients from the same regression, that is take  $$ \frac{\beta_{11}-\beta_{21}}{sd(\beta_{11}-\beta_{21})} $$   The complication arises due to the fact that both come from different regressions. Note that   $$ Var(\beta_{11}-\beta_{21}) = Var(\beta_{11}) + Var(\beta_{21}) -2 Cov(\beta_{11},\beta_{21}) $$ but since they are from different regressions, how would I get $Cov(\beta_{11},\beta_{21})$?  This led me to ask this question here. This must be a standard procedure / standard test, but I cound not find anything that was sufficiently similar to this problem. So, if anyone can point me to the correct procedure, I would be very grateful!
Can not switch Node.js to a default version of my choice How to measure correlation between multi-item likert scales? I recently conducted a online survey and are now having trouble deciding for the right analysis method. For example: I wanted to see if there is a correlation between Factor A and Factor B. However in my survey I did not ask the participants to directly rate Factor A and Factor B, but rather asked multiple subquestions for these two factors which were rated from 5(Strongly Agree) to 1 (Strongly Disagree). I created a sum score for item A and a sum score for item B by summing up the values of each subquestion and calculated the mean of the sumscores to measure them. So my question ist: Which method would be best to use here? I want to test if e.g. people with a higher score in Factor A would be more likely to decide for Factor B. I actually planned using Spearman or ANOVA depending on the number of independent variables, but I am not sure if that would really be the correct way to measure the correlation. How can a distribution have infinite mean and variance? Where does the word "torsion" in algebra come from? Torsion is used to refer to elements of finite order under some binary operation. It doesn't seem to bear any relation to the ordinary everyday use of the word or with its use in differential geometry (which relates back to the ordinary use of the word). So how did it acquire this usage in algebra?  I'm interested to understand the intuition behind why the word "torsion" was chosen for this notion, as well as when it was first used. Could 'cogito ergo sum' possibly be false? Why is everybody so concerned about etc/passwd? Here is the content of my vagrant machine of this particular file:  root:x:0:0:root:/root:/bin/bash daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin bin:x:2:2:bin:/bin:/usr/sbin/nologin sys:x:3:3:sys:/dev:/usr/sbin/nologin sync:x:4:65534:sync:/bin:/bin/sync games:x:5:60:games:/usr/games:/usr/sbin/nologin man:x:6:12:man:/var/cache/man:/usr/sbin/nologin lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin mail:x:8:8:mail:/var/mail:/usr/sbin/nologin news:x:9:9:news:/var/spool/news:/usr/sbin/nologin uucp:x:10:10:uucp:/var/spool/uucp:/usr/sbin/nologin proxy:x:13:13:proxy:/bin:/usr/sbin/nologin www-data:x:33:33:www-data:/var/www:/usr/sbin/nologin backup:x:34:34:backup:/var/backups:/usr/sbin/nologin list:x:38:38:Mailing List Manager:/var/list:/usr/sbin/nologin irc:x:39:39:ircd:/var/run/ircd:/usr/sbin/nologin gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/us$ nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin syslog:x:100:103::/home/syslog:/bin/false   Could anybody explain me why it is bad if some evil guy could get this file of my production server? Loop doesn't see value changed by other thread without a print statement How to make hair material different from the plane itself? In Cycles Render, I added hair to a plane (as I was making a grass field) and I don't seem to know how to make the actual flat plane's material different from the hairs themselves, because I'd like to make the plane have an image texture and the hairs have a yellow-like color to them, but of course, if I attempt to make the material yellow-ish, the plane AND the hairs will become yellow. I'm done with the plane, I just want to control the hairs' materials. Top-bar hat misplaced Sylow 2-subgroups of the group $\mathrm{PSL}(2,q)$ What is the number of Sylow 2-subgroups of the group $\mathrm{PSL}(2,q)$? How can I add a new value to a picklist using APEX? I have queries pulling all of the information correctly but what I can't seem to find was a way to add new options to a picklist using APEX.  I currently have   Package__c.Products__c.add(new Schema.PicklistEntry(products[j].Name));   Package__c is my custom object, and Products__c is the picklist. products[j] is pulling a list of products pulled from our products page.  And I've tried adding it as a select option, or even casting the variable type.  And this information has to go to the actual picklist within a custom object, and not within a visual force page or anything like that. Over time, I've noticed an increasing practice among moderators of the smaller sites (i.e. not in the Trilogy) to move extended comment chains to chat, just because they're too long. Is this a good idea? In the past, I've taken the position on many occasions that I believe that comments serve two purposes only: clarification, and asking for clarification.  I take this position because as a mod I want the freedom to purge a comment trail that is clearly running off the rails without having to argue with anyone about politeness definitions. But that's not the same thing as two pedantic C++ language lawyers debating the finer points of &quot;undefined behavior.&quot;  I give wide latitude to such discussions, as long as the participants don't start throwing spears, because I believe they are instructive. The SE software even has accommodations for this.  Long comment chains are automatically collapsed, so as not to disrupt the Q&amp;A format of the post.  And moving a comment chain to chat is not even a move, really; to do an actual move, you have to perform the conversion, and then delete all of the copied comments from the post. Here is a recent example:  and it's accompanying . What I find amusing is that the OP's detailed POV about the term, where he floats a theory about why everyone thinks that &quot;bugged&quot; is not a thing (that conversation took place in the comments, and is now safely sequestered in the chat room) gets to stay prominently featured in his question, at the very top of the post. Now you could argue that the chat room is a better environment to have these discussions anyway, and you'd be right.  I could argue that if we're going to do that, then why not just automatically convert long discussions to chat rooms? The problem is not so much where the comments reside.  I don't understand why mods are taking it on themselves to fix something that isn't hurting the site (at least in my opinion).  In addition, every time I see this happen, the participants in the conversation immediately lose interest in it.  The only comment that was posted in that room after all the comments were moved is most likely this one:  It wouldn't surprise me if the folks using &quot;bugged&quot; to refer to a certain software quality are the same folks who refer to their programs as &quot;codes&quot; and who believe textspeak is the pinnacle of modern English.  Which nobody will ever see. :) Some mods are really aggressive about this.  I discussed this with a mod on Physics, and he told me that they routinely move discussions when they think they might run off the rails. Intuition of the meaning of homology groups Definition of the $Q$ factor? According to Wikipedia, the  is defined as:  $$Q=2\pi\frac{\mathrm{energy \, \, stored}}{\mathrm{energy \, \,dissipated \, \, per \, \, cycle}}.$$  Here are my questions:   Does the energy dissipated per cycle assume that the amplitude is constant from one cycle to the next. Is it always calculated at the resonance frequency? If the answer to 2 is yes can you explain why for a forced oscillator system with a damping coefficient of $\gamma$ and natural frequency $\omega_o$ the quality factor is $Q=\omega_o/\gamma$ and not some more complicated expression involving the actual resonant frequency (which is not quite $\omega_o$  and is given by $$\omega_r=(\omega_0^2-\frac{\gamma^2}{2})^{\frac{1}{2}}$$ of the system? Is this just an approximation i.e. are we assuming that it resonates at $\omega_o$ but in fact the actual expression is a big more complicated?   Edit: With using the actual value of $\omega_r$ I get: $Q=(\omega_0^2-\frac{\gamma^2}{2})^{\frac{1}{2}}/\gamma$  is this more correct? Good-morning Math Exchange (and good evening to some!)  I have a very basic question that is confusing me.   At school I was told that $\sqrt {a^2} = \pm a$  However, does this mean that $\sqrt {a^2} = +2$ *and*$-2$ or does it mean: $\sqrt {a^2} = +2$ *OR*$-2$  Is it wrong to say 'and'? What are the implications of choosing 'and'/'or'  Any help would be greatly appreciated. Thanks in advance and enjoy the rest of your day :) Shell's process group ID = foreground job's process group ID? I decisively conclude that Shell's process group ID = foreground job process group ID from the 2 sources below. When a background job is selected to run in the foreground, is it the shell's process group ID that changes to the foreground job's process group ID or the reverse?  1.     To facilitate the implementation of the user interface to job control, the operating system maintains the notion of a current terminal process group ID. Members of this process group (processes whose process group ID is equal to the current terminal process group ID) receive keyboard-generated signals such as SIGINT. These processes are said to be in the foreground. Background processes are those whose process group ID differs from the terminal’s; such processes are immune to keyboard-generated signals.    2.        Addition:  $sleep 3000 &amp; $sleep 2000 &amp; $ps xao pid,ppid,pgid,sid,tty,comm | grep tty  PID     PPID    PGID    SID     TTY     COMMAND 1153    1135    1153    1153    tty1    bash 1173    1153    1173    1153    tty1    sleep 1189    1153    1189    1153    tty1    sleep 1219    1153    1219    1153    tty1    ps 1220    1153    1219    1153    tty1    grep Give each site a parallel site for polling, recommendations and subjective-ish stuff Stuff like polls, recommendations based on subjective constraints, puzzles, webcomics etc. do not belong on the serious main SE sites, where professionals should be considered at work and having just a few spare minutes ("code's compiling") to answer questions, so they should not be distracted by such things. However, I'd also like to have a home for these things still using the SE engine. For the reason I mentioned before, this needs to be a separate place though. Let's call it four.[sitename-here].com. A potentially dangerous Request.Form value was detected from the client Every time a user posts something containing &lt; or &gt; in a page in my web application, I get this exception thrown.  I don't want to go into the discussion about the smartness of throwing an exception or crashing an entire web application because somebody entered a character in a text box, but I am looking for an elegant way to handle this.  Trapping the exception and showing     An error has occurred please go back and re-type your entire form again, but this time please do not use &lt;   doesn't seem professional enough to me.  Disabling post validation (validateRequest="false") will definitely avoid this error, but it will leave the page vulnerable to a number of attacks.  Ideally: When a post back occurs containing HTML restricted characters, that posted value in the Form collection will be automatically HTML encoded. So the .Text property of my text-box will be something &amp; lt; html &amp; gt;  Is there a way I can do this from a handler? I am trying to perform a multiple regression in R. However, my dependent variable has the following plot:    Here is a scatterplot matrix with all my variables (WAR is the dependent variable):    I know that I need to perform a transformation on this variable (and possibly the independent variables?) but I am not sure of the exact transformation required. Can someone point me in the right direction? I am happy to provide any additional information about the relationship between the independent and dependent variables.  The diagnostic graphics from my regression look as follows:    EDIT  After transforming the dependent and independent variables using Yeo-Johnson transformations, the diagnostic plots look like this:    If I use a GLM with a log-link, the diagnostic graphics are: I got my Galaxy S4 today (i337M), it's wayyy better than my old SII hehe.  I immediately removed the stock Bell firmware and put the latest snapshot available from CyanogenMod.  I'm wondering if it's possible to convert apps like S Planner, S Note, S Health to CyanogenMod.  Current stock android version available for i337M is 4.2.2. Latest Android version for CM is 4.4.  If I install CM 4.2, can I import/install the APKs and then upgrade to 4.4?  Hope you'll be able to help me :)