2
votes
0answers
44 views
+50

Is Independent jeffreys prior different from independent reference prior?

I have a model involving two scalar parameters $\theta_1$ and $\theta_2$ and derive the Jeffreys prior for $\theta_1$ and $\theta_2$ independently (so for, e.g. $\pi(\theta_1)$, setting in the ...
168
votes
2answers
27k views
+50

How to understand the drawbacks of K-means

K-means is a widely used method in cluster analysis. In my understanding, this method does NOT require ANY assumptions, i.e., give me a dataset and a pre-specified number of clusters, k, and I just ...
3
votes
2answers
73 views
+50

Proper way to test hypothesis of random selection?

Suppose I have $N$ urns, each containing various mixes of red and green balls. A subject is to make a random selection without replacement of $M$ balls from each of the urns, whereupon a count is made ...
24
votes
3answers
11k views
+100

What is difference-in-differences?

Difference in differences has long been popular as a non-experimental tool, especially in economics. Can somebody please provide a clear and non-technical answer to the following questions about ...
67
votes
7answers
16k views
+200

Obtaining knowledge from a random forest

Random forests are considered to be black boxes, but recently I was thinking what knowledge can be obtained from a random forest? The most obvious thing is the importance of the variables, in the ...
8
votes
3answers
147 views
+50

How to analyze trend in non-periodic time series

Suppose I have following non-periodic time series. Obviously the trend is decreasing and I would like to prove it by some test (with p-value). I am unable to use classic linear regression due to ...
0
votes
1answer
42 views
+50

Time series analysis: since volatility depends on time, why returns are stationary?

I run Dickey Fuller test in order to know if stock returns are stationary. I get that no matter which stock I take, his return is stationary. I don't know why I get this result since it is clear that ...
81
votes
9answers
6k views
+400

What is a data scientist?

Having recently graduated from my PhD program in statistics, I had for the last couple of months began searching for work in the field of statistics. Almost every company I considered had a job ...