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STDEV or STDEVP in this case?

  1. Nov 8, 2014 #1
    I'd really appreciate some help. I don't know whether or not I should use STDEV or STDEVP for the data sets below. The values shown have used STDEV in excel.

    1. The problem statement, all variables and given/known data

    In a laboratory, researchers have treated human adrenocortical cells with Corticotropin Releasing Hormone (CRH), in a concentration- and time-dependent manner. Upon completion of the experiment, media from the cell cultures were collected and cortisol levels were measure using a specific radioimmunoassay (as pmol/106 cells).

    The data obtained were:
    Table (1): the levels of cortisol in pmol/106 cells secreted by the adenocortical cells treated with CRH and Basal cells (untreated with CRH) at different times

    Time 6 hours 12 hours 24 hours 36 hours
    Basal CRH Basal CRH Basal CRH Basal CRH
    330 340 330 490 340 710 340 710
    400 400 350 510 280 730 340 770
    380 300 380 440 350 740 355 710
    300 390 360 450 270 730 335 600
    280 330 330 510 370 750 320 710
    300 320 350 510 380 600 310 720
    310 330 320 600 290 710 320 680
    340 290 330 530 400 630 300 710
    330 310 290 400 320 625 340 600
    390 370 350 580 390 570 360 720

    Average 336 338 339 502 339 679.5 332 693
    Standard Deviation 39.2938 35.4401 23.4307 58.1034 44.8219 62.7077 18.1934 51
    T-Test 0.910990159 5.22193E-06 3.80662E-10 3.7809E-10

    Table (2): the levels of cortisol in pmol/106 cells secreted by the adenocortical cells treated with different concentrations of CRH and Basal cells (untreated with CRH)

    Concentration Basal 0.01 nM 0.1 nM 1 nM 10 nM 100 nM 1000 nM
    335 320 390 560 650 710 690
    320 330 400 400 710 690 600
    335 350 330 590 550 680 780
    375 390 410 500 660 710 660
    330 300 420 540 560 660 650
    340 390 360 560 610 670 710
    310 310 390 520 700 710 680
    390 310 330 700 600 650 700
    340 400 350 580 590 720 730
    270 280 420 630 670 700 710

    Average 334.5 338 380 558 630 690 691
    Standard Deviation 31.261 40.1995 33.1662 75.4718491 53.29165 22.8035085 46.141088
    T-Test 0.8391 0.00779 2.8889E-06 5.539E-10 3.2771E-15 2.2107E-12

    The questions:

    Plot the following for both sets of experiments: Effect of time on cortisol secretion after treatment with CRH (100 nM). Would I then plot the means calculated for each cortisol secretion against each time (6,12, 24, 36)?
    Indicate significance (p<0.05) using Students T-Test against Basal levels (i.e. cells that were untreated with a hormone) and also between the different time- and dose-points.


    2. Relevant equations


    3. The attempt at a solution
     
  2. jcsd
  3. Nov 8, 2014 #2

    jedishrfu

    Staff: Mentor

    Welcome to PF!

    Please take some time to read the site guidelines before posting. It's good you used the homework template but what's bad is that you didn't provide any relevant formula so we can't tell you knowledge level and what's even worse is that you didn't even show any work so we don't know where you are stuck.

    We don't do student homework we only provide suggestions and allow the student to solve the problem and to ask questions so they can learn the material better.

    And lastly don't post the same post twice as you've done here.
     
  4. Nov 8, 2014 #3
    I'm unsure as to what you mean by "relevant formula". I provided 2 sets of data and queried as to whether or not STDEV or STDEVP would be the appropriate formula to use in this case.

    Again, I don't understand what you mean by "knowledge level". It's very clear that this is a question relating to the use of formulae in excel.

    I have shown all of the work necessary for the question. The result of the mean and STDEV calculations. I've communicated that I used STDEV to find the results shown in the original post.

    I have not asked for anybody to "do student homework" for me. I have collected the data myself and completed all the relevant calculations. I have asked for suggestions relating to which formula is the most appropriate to use for the data I have calculated.

    I only posted the thread twice as I was unsure as to which section it was most relevant to. Consequently, I felt it best to point in both. I will remove the other thread if you deem it to be cluttering the site.
     
  5. Nov 8, 2014 #4

    Mark44

    Staff: Mentor

    Since this is sample data, use STDEV. The other one, STDEVP, is for the population standard deviation.
     
  6. Nov 8, 2014 #5
    Thanks a lot for your help, Mark.
     
  7. Nov 8, 2014 #6

    jedishrfu

    Staff: Mentor

    My apologies, as I read your full post it looked like you were asking us to solve the whole thing and we can't in good conscience do that here.

    In any event, I'm glad that Mark44 answered your question. Thanks Mark44
     
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