Including additional variable, the variable of interest becomes insignificant I am examining BMI effect on wage. I have included a lot of explanatory variables in the regression and all (most) coefficients were significant, but once I add ability which correlates with education (already in regression) slightly (34%) BMI measures turn insignificant.   Here is the question, what does it mean if BMI turns insignificant once we add another variable in the regression?   Estimated by OLS, cross sectional. Adj R  0.60, F=160.   PS: I added a variable and variable of interest turned insignificant, not vice versa.  Thank you for all the examples below, they address the same topic, but different issue.
How can adding a 2nd IV make the 1st IV significant? I have what is probably a simple question, but it is baffling me right now, so I am hoping you can help me out.  I have a least squares regression model, with one independent variable and one dependent variable. The relationship is not significant. Now I add a second independent variable. Now the relationship between the first independent variable and the dependent variable becomes significant.  How does this work? This is probably demonstrating some issue with my understanding, but to me, but I do not see how adding this second independent variable can make the first significant.
Should flour be thrown out past its expiry date? I just bought a Ryanair plane ticket except that I did not see the QR code on the boarding pass, is that normal? the message is &quot;&quot;. thank you. What is the value of $1^i$? What is the value of $1^i$? $\,$ How do I add a .sty file to my MacTeX/TeXShop installation? I've searched online, but I have not found any clear instructions how to permanently add .sty files to my TeXShop installation. I'm using a Mac with OSX (TeXShop is a mac only program).  What is the best way of doing this? The one comprehensive set of instructions I found .   I've got as far as extracting the files (running LaTeX on the .ins and . dtx files) but after that I don't know what to do. I also don't understand how to update the index of my distribution, and whether there are particular OSX specifics (the instructions are for Windows). Why is you subjective? (Catchy title, eh?)  I am asking the following on the photo.SE site:     How do you change from portrait to landscape in Lightroom   DANGER! DANGER! This appears to be subjective and is likely to be closed.  If I ask the following radically different question:     How do I change from portrait to landscape in Lightroom   ... there is no problem.  So, like the title says: Why is "you" subjective?  (And  where Jeff spills the regex) Sometimes we read books rather quickly and don't give them much (or any) thought, so the action 'reading' does not necessarily imply that we have given enough thoughts to any book we read.   Is there a word that describes reading a book with great care; usually but necessarily slowly over a long period of time. Ball motion with air resistance coupled differential equation for fourth-order Runge-Kutta I've created a MATLAB function for solving coupled differential equation with the fourth-order Runge-Kutta method based on what is provided  (Simultaneous Equations of First Order). Here the function:  function [y] = rk4_c(f, g, h, x, y, z, n) % Runge-Kutta % Implementation of the fourth-order method for coupled equations % h = dt % x is the time here  for ii=1:(n-1)     k1 = h * f(x(ii), y(ii), z(ii));     l1 = h * g(x(ii), y(ii), z(ii));     k2 = h * f(x(ii) + 0.5*h, y(ii) + 0.5*k1, z(ii) + 0.5*l1);     l2 = h * g(x(ii) + 0.5*h, y(ii) + 0.5*k1, z(ii) + 0.5*l1);     k3 = h * f(x(ii) + 0.5*h, y(ii) + 0.5*k2, z(ii) + 0.5*l2);     l3 = h * g(x(ii) + 0.5*h, y(ii) + 0.5*k2, z(ii) + 0.5*l2);     k4 = h * f(x(ii) + h, y(ii) + k3, z(ii) + l3);     l4 = h * g(x(ii) + h, y(ii) + k3, z(ii) + l3);     y(ii+1) = y(ii) + (1/6)*(k1 + 2*k2 + 2*k3 + k4);     z(ii+1) = z(ii) + (1/6)*(l1 + 2*l2 + 2*l3 + l4); end   I would like to use this function for solving motion equations for a ball with air resistance. So starting with the basic equations (I hope they are correct): $$md^2x/dt^2 = F_{D_x}$$ and $$md^2y/dt^2 = F_{D_y}-mg$$ with $$F_{D_x} = -Dvvcos(\theta)$$ and $$F_{D_y} = -Dvvsin(\theta)$$ where $D$ is a drag coefficient. From my understanding, and from what I read, both second-order equation can be converted to two coupled equations that could be used with my coupled Runge-Kutta method function. Can someone help me understand how to convert my equation to a set of coupled equations that could be used with my MATLAB function?  EDIT  I was able to use my rk4_c function, however it only works for solving the velocities. I'm now trying to see how I could solve for the positions x and y. I'm kind of learning about Runge-Kutta methods at the same time, so sorry for the questions that may sound trivials.  % Runge Kutta code to solve projectile motion with quadratic drag % dVx/dt = -(D/m)*vx*sqrt(vx^2+vy^2) % dVy/dt = -(D/m)*vy*sqrt(vx^2+vy^2) - g  clc clear all  % Constant D = 0.24; % m = 2; % kg g = 9.80665; % m/s^2  % Define function handles fVx = @(t,vx,vy) -(D/m)*vx*sqrt(vx^2+vy^2); fVy = @(t,vx,vy) -(D/m)*vy*sqrt(vx^2+vy^2) - g;  % Initial conditions v0 = 200; % m/s theta = 30*pi/180; % rad t(1) = 0; vx(1) = v0*cos(theta); vy(1) = v0*sin(theta);  % Step size h = 0.01; % s tFinal = 2; N = ceil(tFinal/h);  % RK4 simultaneous coupled loop for ii = 1:N     % Update time     t(ii+1) = t(ii) + h;      % Update vx and vy     k1 = h * fVx(t(ii), vx(ii), vy(ii));     l1 = h * fVy(t(ii), vx(ii), vy(ii));     k2 = h * fVx(t(ii) + 0.5*h, vx(ii) + 0.5*k1, vy(ii) + 0.5*l1);     l2 = h * fVy(t(ii) + 0.5*h, vx(ii) + 0.5*k1, vy(ii) + 0.5*l1);     k3 = h * fVx(t(ii) + 0.5*h, vx(ii) + 0.5*k2, vy(ii) + 0.5*l2);     l3 = h * fVy(t(ii) + 0.5*h, vx(ii) + 0.5*k2, vy(ii) + 0.5*l2);     k4 = h * fVx(t(ii) + h, vx(ii) + k3, vy(ii) + l3);     l4 = h * fVy(t(ii) + h, vx(ii) + k3, vy(ii) + l3);     vx(ii+1) = vx(ii) + (1/6)*(k1 + 2*k2 + 2*k3 + k4);     vy(ii+1) = vy(ii) + (1/6)*(l1 + 2*l2 + 2*l3 + l4); end  % Plot the solution figure(1) plot(t, vx, t,vy) xlabel('Time (s)') ylabel('Velocities (m/s)') legend('Vx', 'Vy') I have read the thread regarding , but it does not answer my question.  I am confused about the notation for change in Physics. In Mathematics, $\delta$ and $\Delta$ essentially refer to the same thing, i.e., change. This means that $\Delta x = x_1 - x_2 = \delta x$. The difference between $\delta$ and $d$ is also clear and distinct in differential calculus. We know that $\frac{dy}{dx}$ is always an operator and not a fraction, whereas $\frac{\delta y}{\delta x}$ is an infinitesimal change.   In Physics, however, the distinction is not as clear. Can anyone offer a clearer picture? How can I match multiple occurrences with a regex in JavaScript similar to PHP's preg_match_all()? I am trying to parse url-encoded strings that are made up of key=value pairs separated by either &amp; or &amp;amp;.   The following will only match the first occurrence, breaking apart the keys and values into separate result elements:  var result = mystring.match(/(?:&amp;|&amp;amp;)?([^=]+)=([^&amp;]+)/)   The results for the string '1111342=Adam%20Franco&amp;348572=Bob%20Jones' would be:  ['1111342', 'Adam%20Franco']   Using the global flag, 'g', will match all occurrences, but only return the fully matched sub-strings, not the separated keys and values:  var result = mystring.match(/(?:&amp;|&amp;amp;)?([^=]+)=([^&amp;]+)/g)   The results for the string '1111342=Adam%20Franco&amp;348572=Bob%20Jones' would be:  ['1111342=Adam%20Franco', '&amp;348572=Bob%20Jones']   While I could split the string on &amp; and break apart each key/value pair individually, is there any way using JavaScript's regular expression support to match multiple occurrences of the pattern /(?:&amp;|&amp;amp;)?([^=]+)=([^&amp;]+)/ similar to PHP's preg_match_all() function?  I'm aiming for some way to get results with the sub-matches separated like:  [['1111342', '348572'], ['Adam%20Franco', 'Bob%20Jones']]   or   [['1111342', 'Adam%20Franco'], ['348572', 'Bob%20Jones']] It's time for drag and drop! I often find myself wishing SO supported drag and drop. For example I drag a tag to my favs and it would add it, or when searching by tag I would like to drag the tag to the search box and get [asp.net] added in the search box.   Does it make sense to add this feature or is it just too much work for so little use? Gaming with Virtualbox, has it worked for you? Currently I am using Windows 8. I have a virtual box with Ubuntu set up for development. Aside from that I sometimes just want to relax and enjoy a game (Battlefield 3, Skyrim, Saints Row: The Third, etc) after hours of research and development.   I want to have my main machine with linux, and install windows on a virtual box.   What I want to know, from those who have tried or seen it:   How is the performance? I've never been clear on this but, even if I install the correct drivers on the windows box, will it matter? At least on this part, I'm just curious how it offload. Which drivers will matter the most.  Mouse and Keyboard integration, I'll be honest, sometimes the mouse integration in Virtual Box is a bit frustrating, mouse cursor disappears, etc.    I'm not sure if this is the right place to ask. I'm merely trying to come back to linux, yet I'm a PC gamer so I can't throw away Steam. I'm aware of the linux client, but most of those games won't work.   If there's a right place to ask this whether StackExchange sites or any other site let me know.   Cheers and I hope those in the same position find a middle ground. Preserving signatures of decorated functions Wrong pluralization on accounts tab of user profile Under accounts tab of a user's profile, words questions and answers are used even when count is 1. For live example, you can go to my profile &amp; click accounts tab. Scroll down to Drupal Answers row where you can find &quot;1 answers&quot; which should be &quot;1 answer&quot;. Or, scroll down to Server Fault row to see both &quot;1 questions&quot; and &quot;1 answers&quot;. Take as an example the well-known . In the original paper, the regression model was used to model the amount people were willing to pay for improved air quality.  But the 'people' whose behaviour was being modelled was never specified. Presumably, it was not limited to 'residents of Greater Boston'. Only implausibly would it be 'humans anywhere on the planet'. Nor, 'all US residents'.   So what inference are we invited by the authors to draw about the scope they intend for their theory? Perhaps 'all residents of large US metro areas'. But - what about other First World metro areas? The first two sections of the Boston paper scrupulously avoid any reference which might suggest that they had a particular 'population' to which their 'sample' was to apply.  There is also the dimension of time - the data came from the 70s, whereas the theory is has no time limitations spelt out.  Plus - going back to first principles - how could the Boston data be treated as a sample of a population including, say, the Chicago metro area when no data from the Chicago area was considered?   Besides, lots of the covariates in the Boston regression weren't samples at all, but totals - so, for example, the proportion of blacks was supplied from census stats.  My question: how can we conceive the Boston data as supporting the geographically unlimited propositions in the paper? Is there a mathematical way of showing equivalence or approximation of the Boston data analysis to other cities? Or is it just assumed as a matter of common sense - such that the paper's authors would be amazed to think anyone could have any doubts on the matter? Do not disturb mode - but allow certain apps In my past experiences, I have almost never typeset my manuscripts according to the formats required by the journals to which I would like to submit. I leave my manuscripts as produced by the LaTeX article documentclass.  Recently I am wondering: Would such a behavior generally give handling editors a negative first impression? Linux, find all files matching pattern and delete Looking to find all files (recursively) which have an underscore in their file name and then delete them via command line. Batch Convert Images from One Format to Another while maintaining directory structure, and removing originals I've looked at , and while it works there a few issues:   All converted images are placed in the directory from which the command is called. The original images are kept.   I need to convert around 70,000 .tif and .jpgs to .pngs.  It's really important the the files when converted are placed in their normal directories.    I can do a batch rm of .tff/.jpg's at the end if that's the best way to handle removing the old files. Page number position Changing Locale within the app itself