# Tagged Questions

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### Is it possible to compare 2 groups while controlling for something?

Is it possible to compare two groups (e.g., t-test, Wilcoxon, Mann-Whitney test, etc.) while controlling for something? E.g., I want to compare home ownership between military veterans and non-...
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### Control group and bias

I am trying to determine the percentage of patients who will continue to refill a drug on a timely basis. I have data for each month how many patients (as a fraction of those who started the treatment ...
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### Lee (1983) sample selection correction with accelerated failure time model (in Stata)

I am trying to replicate the selection control used by Henderson et al. (2006), which is derived from Lee (1983). Henderson et al study CEOs over time and try to control for the likelihood that a CEO ...
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### CHAID control parameters

In CHAID control parameters we have to specify the alpha value for Merging Threshold and Splitting Threshold. Typically this alpha (p-value) is set at 0.05. Assume we are not supposed to keep the ...
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### Calculate statistical significance when control is 0

My question for you guys is; I have a control group that are eating normal food and an experimental group that are only eating a western high fat diet. I wanted to look at how much the experimental ...
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### Multivariable Regression on correlated / collinear variables

Let us consider a variable $Y$ on which we want to apply a multivariable linear regression on the variables $X_1$ and $X_2$. $X_1$ and $X_2$ are collinear by construction, with $X_1=ab$ and $X_2=bc$, ...
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### Correlation analysis with compound variables: controling for a second correlation

We want to test for the existence of a correlation between a variable $X$ and a second variable $Y=ab$ ($a$ and $b$ being independent variables representing observational data). We know that the ...
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### Control variables in instrumental variable regression

I have seen published papers include "exogenous controls" in their instrumental variables regression. Can someone explain: What is meant by "exogenous" in this case? The purpose of these "controls" ...
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### How to interpret linear regression with different categorical variables

I am looking at the effect of 1 categorical dependent variable A (3 outcomes) on 1 independent variable. This is significant. Then I want to see if this effect is still true if I add another ...
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### Control group construction in Synthetic Control Method

I want to use the Synthetic Control Method to estimate the effect of the adaption of a new ballot institution (treatment) on fiscal policy. My sample consists of 20 units observed at 100 time points. ...
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### Difference in difference with pre and post period

I wanted some guidance on some test I am performing. Basically I want to see the difference between the effect of unionisation on 13 countries grouped into 3 that don't have unions and 10 that have ...
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### Controlling for biased audiences in online surveys

For a long time I have been meaning to set up a bunch of online surveys asking a whole range of social questions and publish the results. I am well aware that there are various difficulties to ...
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### Gradient descent for a noisy system

I have a system with tuning parameter $w$. To evaluate this system I use cost function $f(w)$. I try finding the optimum value for $w$ using Gradient Descent starting from $w_0$. The problem with ...
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### Using control charts with very large subgroup size?

I am working with a very large data set -- time-series data from an on-line process monitor with a 10 second measurement interval. I am trying to develop control limits for the process using control ...
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### Can Control Variables also be included as Dependent Variables?

I'm currently reading an academic journal (http://papers.ssrn.com/sol3/papers.cfm?abstract_id=2488863) which, in Table 11 of the paper, lists several control variables including: Returns Size ...
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### Control of assumptions in general linear model

In which ways can I "control" the assumptions I make in a linear model where I have $n$ independent, random variables with same variance and where the mean vector lies in some subspace (a strict ...
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### “Controlling” for multiple sequential association rules?

Assume I have data along the following lines A-A-B-C A-A-B-C A-A-B-C Then I test the following sequential association rule: "A-A precedes C", which is true 100% ...
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### Determining minimum required sample size for control (for purposes of measuring lift)

SO in a sales setting where people can either buy or not buy (i.e. binary response), say I have a treatment that I know (or believe strongly) to be effective. I want to give it to as many people as ...
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### Predictions in a control loop like airconditions

I wonder if there are special things to consider with predictions in a control loop, e.g. An airconditioner trys to hold the target temperature at 20 degrees. I want to predict the energy consumption,...
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### ANCOVA--Introduce second covariate

I am conducting a pretest-posttest ANCOVA with a control group in which I covary the pretest data and use the posttest data as the dependent (Jobs). Time is a repeated measure with 6 pretest and 9 ...
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### Defining the size of control group in chi square statistics

I'm trying to compare the prevalence rate of autism in offspring of mothers with and without gestational diabetes. I gathered data from 1000 women, 8 children have autism (prevalence rate 8/1000). ...
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### Should I control for categorical control variables that are related to my independent variable in panel with many panels, short time length?

I am doing a panel study where I have a sample of persons $i=1...N$ (up to $N=300$), that have some personality dimension quantified as variable $x$, over a time horizon $t=1...T$ (up to $T=20$). From ...
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### Adding control variable to difference-in-difference equation

I'm new to this so bear with me. I'm running a Difference-in-Difference analysis, this is the equation: Yit = α+ β1Treati + β2Postt + β3 (Treat⋅Post)it + ϵit I want to control for a few variables, ...
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### Should I check control variables for robustness?

I am working with count data and using a negative binomial regression. I have 3 core independent variables and control variables (age,education and sex). But the problem is that I have 8 age groups ...
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### Is there a way to test whether or not you're “over-controlling?”

Just got a stats assignment back in which I was told that "many of these regressions are over-controlling." However, each one of the controls were independently statistically significant, so it's not ...
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### Control Variables-Difference in Differences-Repeated Cross Sectional

I have a question regarding control variables in a difference in difference model with repeated cross-sectional data. Is it allowed to add individual level controls while you are looking at group ...
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### Newbie question: can a categorical IV be included in ANCOVA with only a couple observations in 1 group

I think this is a pretty simple question, but I have been unable to find an appropriate answer. Please help. I have identified a sub-sample of my treatment group that were taking a medication that ...
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### Estimating process standard deviation for a quality control chart. What is $s/(c4)$ and how to calculate it in R? [duplicate]

I recently came across quality control charts in my studies and found out that the estimator $$\hat \sigma =s/c4$$ is preferred for UCL and LCL calculations in an x bar chart as it is considered ...
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### Determine Number of Users in Control and Treatment Groups

I need to be able to determine how many users should be in a control group and how many users should be in the treatment group. I have read that it is statistically best to split it 50/50, but with my ...
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### Failure prediction from production line data/ Statistical process control

I'm a research student looking into predicting product defects from on-line time series data. I'm struggling to find exactly which statistics area I should be looking into to create an error ...
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### Remove estimated effect of independent variable on dependent variables (interval/ratio) using linear regression

Question: Can we use unstandardized coefficients derived from linear regression to remove the effect of an independent variable on the dependent variable? I have a large dataset and suspect that an (...
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### Control variables in experiments

Assume you are trying to test the effect of condition X. You sample people randomly and put them in a manipulation group (condition X) and a control group (condition Y). Simultaneously you want to ...
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### Is there a unified form for Process control and process control analysis

I have done some reading (NIST, JMP, PCS, Juran, some JEDEC, ...) and it appears there are four very common general types of control charts: Shewhart (X-bar, R, S) CUSUM (cumulative sum) EWMA (...
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### Which method should be adopted for pretest and posttest research?

My company will hold three types of activities (leisure, family-oriented and interest class) in order to improve the co-worker relationship. I am assigned to use questionnaires (by using the workplace ...
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### Control Chart - Descriptive or Inferential?

Which category of statistics do Control Charts fall under? Descriptive, Inferential, or something else? As I'm thinking out loud...Control Charts use elements of Descriptive (central tendency, ...
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### Can I still call the study placebo controlled if I give the control treatment to the test population as well

I am studying the efficacy of a novel drug in treating a cardiovascular disease with continuous variable results being measured and statistically analyzed. Suppose the control population is getting ...
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### SAS/STAT: Testing the significance for Email Marketing Control groups with Proc Power

I'm trying to figure out a way to test to see if my control groups for email margeling campaigns will produce statistically significant re sluts. The group counts have already been set. The control ...
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### R: Test for correlation with a covariate?

R: I have a linear correlation between two variables x and y, but need to control for a third variable that may be influencing the output. My question is about which test I should/ can use. Can I use ...
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### Interpretation of linear regression where the outcome can only possibly cause the value of predictors and not viceversa

We want the verify the association between artificial pregnancy (artificial insemination) versus natural pregnancy and a series of pregnancy conditions (hypertensions, diabetes, etc). We first ...
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### How find controls limits for CUSUM chart

I am trying to re-do a simulation work in quality control. In this simulation they use bisection search algorithm to find the control limits h (the threshold) that gives the desire average run length ...
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### Interpretation of Model When Intentionally Excluding a Control Variable!

I am looking at factors affecting firm value (the dependent variable). I fitted the following model using OLS: $log(FirmValue_i)=\beta_0 + \beta_1Divers_i+ \beta_2HQLoc_i + \epsilon_i$ where \$...
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### Controlling for age and sex in a multiple regression with a backward model selection

So, I have this dataset with a hormonal measure as independent variable and behavioral measures as dependent variables. I am using a linear regression as my model and after a backward selection, ended ...
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### Q: How to correctly include a categorial control variable in a regression model (in R)?

I'm trying to fit a (logistic) regression model to predict the successful funding of crowdfunding ventures (0/1) based on a series of IV with different level of measurement. One of these IVs is a ...
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### “Controlling” for population/sample sizes when looking at rates?

I have a pretty basic understanding of statistics, so please bear with me: I'm making an index (ranking) of sector performance I am including indicators such as "Percent of profitable firms in ...
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### Best statistics to show outliers beyond 2 SD

I try to perform scheduling for an organization based on client flows. We are very seasonal. Our senior management in Washington, DC make us base our schedule on the mean number of clients we have ...
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### In two places at once: treatment and control groups

When performing a treatment study (e.g. a difference-in-differences design) in multi-dimensional panel data (e.g., firm-individual-time, bank-firm-time, etc.) is it ok if the "smaller" cross-sectional ...
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### propensity score matching and difference in difference

I am trying to analyse the impact of a cash stipend program, onto child learning outcomes. I have first modeled the conditional probability of each student receiving this program. So basically I have ...
1k views

### Logistic Regression- Control Variable Not significant In Model 2

I am new to this site and it's my first post, so my apologies in advance if I have made any mistakes or did not follow proper etiquette. I am running a logistic regression analysis with six predictor ...
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### Comparing Binomial Success Parameters in a Stratified Approach - An Example in Biostatistics

I would like to contrast the effectiveness of drug treatment and surgical treatment in a study with the following data. Each row represents one trial, and each trial uses either drugs or surgeries to ...
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### Control chart constants [closed]

When calculating Upper Control Limit (UCL) and Lower Control Limit (LCL) in control charts I use constants from http://web.uni-plovdiv.bg/kiril/Students/Masters-MYK/table_of_control_chart_constants....