Work out Cronbach's alpha for a questionnaire scale ALPHA
Paste the item scores straight from a spreadsheet, a row per person. You get alpha, each item's correlation with the rest, alpha without it, and a flag on any item that looks as if it was never reversed.
The item scores
Paste from a spreadsheet: columns split on tabs, commas or spaces. A first row of names is used as the item names. An empty cell, or anything that is not a number, counts as unanswered.
The result
For the write-up
How it works
ALPHA reads a header row of item names if there is one, reverse-scores the items you name before it starts, and leaves out anybody with an item unanswered, saying how many. Every figure is held to the textbook formulas worked in NumPy, and nothing typed here leaves this tab.
What it does, and what it does not
Cronbach's alpha is the most reported figure for whether the items of a questionnaire scale hang together: whether people who score high on one item tend to score high on the others. It is worked out here from the items' variances and the variance of the total, the same formula SPSS and every textbook use, and the item table shows the corrected item-total correlation (each item against the total of the others, not including itself) and alpha with each item left out.
Alpha is not a measure of whether a scale measures one thing, and it is not validity. It assumes each item measures the same thing equally well; when they do not, McDonald's omega, from a factor analysis, is the better estimate, and this page does not work it out. It gives no confidence interval for alpha. It does not reverse items by itself: it flags one that looks reversed and leaves the decision with you.
The figures are held, in this site's own tests, to the same formulas worked in NumPy on four scales, one with an item deliberately left unreversed. To describe one item's answers, FIGURES does that.
Doing this often? OBSCURA Research works out alpha on the items of a whole questionnaire file, beside factor analysis, with the output saved to Word or PDF. On its own, US$2 a month; with everything else, US$5 a month or US$48 a year. 7 days free.