Difference between revisions of "Variations in means/statistical calculations"
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Means, the most common statistical calculation, and some other calculations sometimes appear a little differently in mTAB vs other packages such as SPSS, or even show up just as zeros. The zero occurrence can be easily taken care of, especially in the short term and the numbers varying slightly can usually be dealt with as easily. | Means, the most common statistical calculation, and some other calculations sometimes appear a little differently in mTAB vs other packages such as SPSS, or even show up just as zeros. The zero occurrence can be easily taken care of, especially in the short term and the numbers varying slightly can usually be dealt with as easily. | ||
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| + | '''How are Means Calculated?''' | ||
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| + | Each response to a numeric question is usually associated by mTAB with a statistical value or range. If the response to a question is 100, then usually the statistical value would also be 100. | ||
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| + | However, ranges work differently and there are two kinds of range questions. Some range questions come that way from the survey itself. For example, respondents are asked what income range they fall into. | ||
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| + | '''How does it work''' | ||
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| + | Ranges work. | ||
Revision as of 17:35, 8 August 2013
Means, the most common statistical calculation, and some other calculations sometimes appear a little differently in mTAB vs other packages such as SPSS, or even show up just as zeros. The zero occurrence can be easily taken care of, especially in the short term and the numbers varying slightly can usually be dealt with as easily.
How are Means Calculated?
Each response to a numeric question is usually associated by mTAB with a statistical value or range. If the response to a question is 100, then usually the statistical value would also be 100.
However, ranges work differently and there are two kinds of range questions. Some range questions come that way from the survey itself. For example, respondents are asked what income range they fall into.
How does it work
Ranges work.
How Are Means Calculated?
Each response to a numeric question is usually associated by mTAB with a statistical value or range. If the response to a question is 100,thenusuallythestatisticalvaluewouldalsobe100.However,rangesworkdifferentlyandtherearetwokindsofrangequestions.Somerangequestionscomethatwayfromthesurveyitself.Forexample,respondentsareaskedwhatincomerangetheyfallinto.TheotherkindofrangequestionisthekindweimplementhereatmTAB.Forexample,ifarespondentisaskedtowriteinhisincomeinthousands,youdonotwanttolookateverybreakof1,000. That is a useless amount of detail, especially in higher income brackets, so we cluster the respondents into ranges that are more useful. Our older ranges would automatically give ANY respondent who falls between 100,000and150,000 a statistical value of 125,000 even if 90% of these people actually fall in the 100,000to120,000 range. This would obviously skew the numbers. In older databases, there is nothing that can be done about that unless you want to guess where these respondents fall and then manually alter the stat values. This may be useful sometimes when the last response to a question is "100,000ormore."Inacaselikethistheupper(righthand)statvaluemaybehigherorlowerthansomeonewhoknowsthedatawellwouldwant.″Innewerdatabases″,wehaveanewwayofhandling"fillintheblank"stylequestionswhichweputintorangeswhichwecall"ValueFields".Thisvaluefieldputstherespondentsintotherangetheybelonginasbefore,butrememberstheexactdatavaluetheyprovidedaswell,forcalculatingmeans.ThisabilitywasintroducedinSeptember1997andisnowbeingusedinallstudiesandimplementedinoldertrackingstudiesastimepermits.Ifaquestionusesavaluefield,editingthestatvaluesdoes″not″changethestatisticalcalculations.‴FixingZerosOrChangingStatValues‴[[File:Sig−testingvariations−in−meanssubset.jpg|thumb|right|x350px]]Firstoff,thequestionyouaretryingtofindameanforshouldhavesomenumericstatisticalvalueassociatedwithit.Ifitdoes,thensetupyourtabasusual.Whenyouarefinishedsettingupyourtab,gotothesubsetwindowforthequestionthatyouarenotgettingameanfor.Inthiswindowyouwillseeontheleftalistofresponsessuchas"100" or "100−200". On the right you should notice two empty columns. Just click on the first empty column to the right of 100forexampleandtypein100thenhitenter.Orifitwasarangelike100-$200 you should type 100 in the first column to the right of that response, and 200 in the second column. Do this for all the responses that need a statistical value. "No Answer" should not have a statistical value associated with it.
Now when you run your tab, you can get means and other statistical calculations.
NOTE: If a question uses a value field, editing the stat values does not change the statistical calculations. The only way to alter the mean for a value field question is to deselect the responses you want left out of the subset window by highlighting a particular response and hitting backspace to put a minus sign by the response. This eliminates it from the sample when you run your tab. If you merely select the responses you want included, subsetting will not work, you can only deselect the responses you do not want.
Ratings/Scoring type questions are usually not value field, fill in the blank number questions usually are.
