Standard Error and confidence interval

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Paola
Paola el 20 de Jul. de 2020
Respondida: Star Strider el 20 de Jul. de 2020
Hello,
I have a 16x31 matrix, DeltaAnglesAdj, and I calculated the Standard error, columnwise:
std_err_mean = std(DeltaAnglesAdj,[],1)/sqrt(size(DeltaAnglesAdj,1)); (1x31 vector)
Then I calculated the P95:
P95 = tinv(0.975, size(DeltaAnglesAdj,1)-1);
How can I calculate the Confidence interval?
when I applied the method found on previous questions on Mathworks, it gives me error:
mean_data = mean(DeltaAnglesAdj,1); (1x31 vector)
CI95 = mean_data + std_err_mean*[-1 1]*P95;
Error using *
Incorrect dimensions for matrix multiplication. Check that the number of
columns in the first matrix matches the number of rows in the second matrix.
To perform elementwise multiplication, use '.*'.
The error persists also after following the instruction:
CI95 = mean_data + std_err_mean*.[-1 1]*.P95;
Error: Invalid use of operator.
How can I solve this?

Respuestas (1)

Star Strider
Star Strider el 20 de Jul. de 2020
The actual problem is that the vectors you are working with are row vectors. To create ‘CI95’ as a (2x31) matrix, you need to code it a bit differently.
Try this:
CI95 = mean_data + std_err_mean.*[-1; 1]*P95;
Then, to plot the mean and confidence intervals:
figure
plot((1:31), mean_data, (1:31), CI95)
.

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