Cronbach's Alpha - SPSS (part 1)

hi welcome to how to stats comm in this video I'm going to demonstrate how to calculate cronbach's alpha in SPSS in fact I'm going to do a little more than that I'm going to do basically a full internal consistency reliability analysis through the various options that are available in SPSS which are basically which can be basically conducted at the same time is calculating cronbach's alpha now just to very briefly cover what chrome maxout cronbach's alpha is when cronbach's alpha is an estimate of the internal consistency associated with the scores that can be derived from a scale or a composite score and reliability is important because in the absence of reliability it's impossible to have any validity associated with with the scales with the scores of a scale that's why it's so important to do it and usually you do this type of analysis before you do any other types of analyses on your data especially if you're combining scores together and basically cronbach's alpha is helping to determine whether it's justifiable to interpret scores that have been aggregated together now in this case I've got some real data from a questionnaire called the Toronto alexithymia scale which is a 20 item inventory and what I'm going to look at specifically is one of the sub scales within the task 20 called external oriented thinking and I'm going to calculate the reliability I'm going to calculate cronbach's alpha and I'm also going to look at some other internal consistency reliability indicators so to calculate the reliability or internal or cronbach's alpha specifically associated with this sub scale I'm going to go in to analyze scale reliability analysis and then I'm going to choose the items that correspond to this specific scale within the 20 item inventory and it's called as I mentioned externally oriented thinking so I'm going to put the first item that's IOT into the items box over here so these are the items that are the total items within your spreadsheet and these are the item that I'm actually going to submit to the analysis so I've got another item there that corresponds to that scale another one we've got the item number sixteen eighteen and nineteen and twenty so let's just make sure we've got yo T all along the items and I'm not missing any okay so now I'm going to go into statistics to click a few options I'll note actually before I do that SPSS has a model option here and alpha is the default there are a few other ones like split half reliability Guttman reliability parallel analysis reliability and strict parallel analysis reliability ninety-five percent of the time people would be interested exclusively in alpha cronbach's alpha but there are a few other options that are very useful and in particular you'd want the descriptives of for the item the scale the scale if item deleted quite important and correlations between the between the items everything else is probably not too important you'd probably find out the means and standard deviations associated with the scale by calculating a sum score so I'm not going to do that in this case but you could do that here if you wanted to all right so I'm going to get descriptors for item scale scale if item deleted which is going to be important in correlations which is also important click OK and then ok then we get the output and let me just get this into a different size all right so the output the first thing that SPSS gives in the output is the number of the sample size and in this case we got 355 people that were included in the analysis and then SPSS gives the chromebox alpha coefficient over here so cronbach's alpha estimated at 0.65 zero and basically that means that 65% of the variability in a composite score by combining those 8 items it's saying here 8 items were submitted to the analysis so if we calculated a composite score to indicate externally oriented thinking 65 percent of the variance in that score would be considered what's called true score variance or reliable internally consistent reliable variance SPSS also spits out the cronbach's alpha based on standardized items and basically the difference between the two is that this second option calculates a chrome box alpha under the pretense that the items all have the same variance and in practice that's usually not the case there'll be some variance in the variances the variances be different a little bit in some cases the difference in most cases cronbach's alpha and standardized cronbach's alpha do not differ very much because people are combining items that roughly have the same standard deviation or variance but sometimes when you're combining dichotomously scored items with ordinal scaled items or interval/ratio items you'll get very big differences between standardized alpha and cronbach's alpha so just to reiterate we got 0.65 zero and what i guess i'll mention very briefly what what are criteria what is the criterion to determine an acceptable level of reliability is actually something that's not been resolved thoroughly there are several recommendations and the most frequently cited recomm

Channel: how2stats

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Keywords: Cronbach's alpha SPSS, reliabilty, reliability test SPSS, SPSS Cronbach, item total statistics, alpha Cronbach

Id: 2gHvHm2SE5s

Length: 6min 4sec (364 seconds)

Published: Thu Sep 15 2011