Identifying if reaction times are 3 standard deviations away from mean

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Rania Hanna 2022-9-19

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https://ww2.mathworks.cn/matlabcentral/answers/1807565-identifying-if-reaction-times-are-3-standard-deviations-away-from-mean

评论： Rania Hanna 2022-9-20

have a data set of several thousand values.

There are 10 unique subj_indx, 1 through 10. Each one represents an experimental subject. Each subject has a bunch of reaction times, rt.

I am new to Matlab and don't understand how to write for loops. I know I need to run through the entire dataset, and identify outlier reaction time trials, without using isoutlier function. This is because I want to be ale to identify whether each RT trial is > 3 standard deviations away from the mean RT, and then mark that trial in a new vector as "1", otherwise, mark it as "0."

I know Matlab has standard deviation and mean functinos, but am not sure how to connect everything together for this code.

I don't know where to start other than:

rt=subject_data.rt;

for id = 1:length(subj_idx)%loop for each unique id value

%rtIdx = 1:length(rt)

currentid = rt(rtIdx);

rtIdx = 0;

and I'm not sure even that's correct.

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Steven Lord 2022-9-20

See the description of the "mean" method on that isoutlier documentation page to which I linked.

Rania Hanna 2022-9-20

Perfect, thanks so much!

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Answer 1

Chunru 2022-9-20

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https://ww2.mathworks.cn/matlabcentral/answers/1807565-identifying-if-reaction-times-are-3-standard-deviations-away-from-mean#answer_1056780

编辑：Chunru 2022-9-20

在 MATLAB Online 中打开

% rt=subject_data.rt;
rt = randn(300, 1) * 3 + 1;         % genate some random data
mu = mean(rt)
mu = 1.2843
sigma = std(rt)
sigma = 3.0914
idx = abs((rt-mu)) > 1*sigma;       % use 3 sigma when samples are large
[rt idx]
ans = 300×2
    2.6351         0
   -0.5263         0
   -1.5895         0
    2.5097         0
    4.4268    1.0000
    1.5017         0
   -3.1915    1.0000
   -1.7580         0
    1.9555         0
    1.5195         0