;% !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ;% ;% Identifier attribute deleted. ;% ;% !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ;% ;% NAME: Sexual activity and the lifespan of male fruitflies ;% TYPE: Designed (almost factorial) experiment ;% SIZE: 125 observations, 5 variables ;% ;% DESCRIPTIVE ABSTRACT: ;% A cost of increased reproduction in terms of reduced longevity has been ;% shown for female fruitflies, but not for males. The flies used were an ;% outbred stock. Sexual activity was manipulated by supplying individual ;% males with one or eight receptive virgin females per day. The ;% longevity of these males was compared with that of two control types. ;% The first control consisted of two sets of individual males kept with ;% one or eight newly inseminated females. Newly inseminated females will ;% not usually remate for at least two days, and thus served as a control ;% for any effect of competition with the male for food or space. The ;% second control was a set of individual males kept with no females. ;% There were 25 males in each of the five groups, which were treated ;% identically in number of anaesthetizations (using CO2) and provision of ;% fresh food medium. ;% ;% SOURCE: ;% Figure 2 in the article "Sexual Activity and the Lifespan of Male ;% Fruitflies" by Linda Partridge and Marion Farquhar. _Nature_, 294, ;% 580-581, 1981. ;% ;% VARIABLE DESCRIPTIONS: ;% Columns Variable Description ;% ------- -------- ----------- ;% 1- 2 ID Serial No. (1-25) within each group of 25 ;% (the order in which data points were abstracted) ;% ;% 4 PARTNERS Number of companions (0, 1 or 8) ;% ;% 6 TYPE Type of companion ;% 0: newly pregnant female ;% 1: virgin female ;% 9: not applicable (when PARTNERS=0) ;% ;% 8- 9 LONGEVITY Lifespan, in days ;% ;% 11-14 THORAX Length of thorax, in mm (x.xx) ;% ;% 16-17 SLEEP Percentage of each day spent sleeping ;% ;% ;% SPECIAL NOTES: ;% `Compliance' of the males in the two experimental groups was documented ;% as follows: On two days per week throughout the life of each ;% experimental male, the females that had been supplied as virgins to ;% that male were kept and examined for fertile eggs. The insemination ;% rate declined from approximately 7 females/day at age one week to just ;% under 2/day at age eight weeks in the males supplied with eight virgin ;% females per day, and from just under 1/day at age one week to ;% approximately 0.6/day at age eight weeks in the males supplied with one ;% virgin female per day. These `compliance' data were not supplied for ;% individual males, but the authors say that "There were no significant ;% differences between the individual males within each experimental ;% group." ;% ;% STORY BEHIND THE DATA: ;% James Hanley found this dataset in _Nature_ and was attracted by the ;% way the raw data were presented in classical analysis of covariance ;% style in Figure 2. He read the data points from the graphs and brought ;% them to the attention of a colleague with whom he was teaching the ;% applied statistics course. Dr. Liddell thought that with only three ;% explanatory variables (THORAX, plus PARTNERS and TYPE to describe the ;% five groups), it would not be challenging enough as a data-analysis ;% project. He suggested adding another variable. James Hanley added ;% SLEEP, a variable not mentioned in the published article. Teachers can ;% contact us about the construction of this variable. (We prefer to ;% divulge the details at the end of the data-analysis project.) ;% ;% Further discussion of the background and pedagogical use of this ;% dataset can be found in Hanley (1983) and in Hanley and Shapiro ;% (1994). To obtain the Hanley and Shapiro article, send the one-line ;% e-mail message: ;% send jse/v2n1/datasets.hanley ;% to the address archive@jse.stat.ncsu.edu ;% ;% PEDAGOGICAL NOTES: ;% This has been the most successful and the most memorable dataset we ;% have used in an "applications of statistics" course, which we have ;% taught for ten years. The most common analysis techniques have been ;% analysis of variance, classical analysis of covariance, and multiple ;% regression. Because the variable THORAX is so strong (it explains ;% about 1/3 of the variance in LONGEVITY), it is important to consider it ;% to increase the precision of between-group contrasts. When students ;% first check and find that the distributions of thorax length, and in ;% particular, the mean thorax length, are very similar in the different ;% groups, many of them are willing to say (in epidemiological ;% terminology) that THORAX is not a confounding variable, and that it can ;% be omitted from the analysis. ;% ;% There is usually lively discussion about the primary contrast. The ;% five groups and their special structure allow opportunities for ;% students to understand and verbalize what we mean by the term ;% "statistical interaction." ;% ;% There is also much debate as to whether one should take the SLEEP ;% variable into account. Some students say that it is an `intermediate' ;% variable. Some students formally test the mean level of SLEEP across ;% groups, find one pair where there is a statistically significant ;% difference, and want to treat it as a confounding variable. A few ;% students muse about how it was measured. ;% ;% There is heteroscedasticity in the LONGEVITY variable. ;% ;% One very observant student (now a professor) argued that THORAX cannot ;% be used as a predictor or explanatory variable for the LONGEVITY ;% outcome since fruitflies who die young may not be fully grown, i.e., it ;% is also an intermediate variable. One Ph.D. student who had studied ;% entomology assured us that fruitflies do not grow longer after birth; ;% therefore, the THORAX length is not time-dependent! ;% ;% Curiously, the dataset has seldom been analyzed using techniques from ;% survival analysis. The fact that there are no censored observations is ;% not really an excuse, and one could easily devise a way to introduce ;% censoring of LONGEVITY. ;% ;% REFERENCES: ;% Hanley, J. A. (1983), "Appropriate Uses of Multivariate Analysis," ;% _Annual Review of Public Health_, 4, 155-180. ;% ;% Hanley, J. A., and Shapiro, S. H. (1994), "Sexual Activity and the ;% Lifespan of Male Fruitflies: A Dataset That Gets Attention," _Journal ;% of Statistics Education_, Volume 2, Number 1. ;% ;% SUBMITTED BY: ;% James A. Hanley and Stanley H. Shapiro ;% Department of Epidemiology and Biostatistics ;% McGill University ;% 1020 Pine Avenue West ;% Montreal, Quebec, H3A 1A2 ;% Canada ;% tel: +1 (514) 398-6270 (JH) ;% +1 (514) 398-6272 (SS) ;% fax: +1 (514) 398-4503 ;% INJH@musicb.mcgill.ca, StanS@epid.lan.mcgill.ca ;% (defun fruitfly () (data :name 'fruitfly :columns '(PARTNERS TYPE $THORAX $SLEEP $class) :egs '( (8 0 35 0.64 22) (8 0 37 0.68 9) (8 0 49 0.68 49) (8 0 46 0.72 1) (8 0 63 0.72 23) (8 0 39 0.76 83) (8 0 46 0.76 23) (8 0 56 0.76 15) (8 0 63 0.76 9) (8 0 65 0.76 81) (8 0 56 0.8 12) (8 0 65 0.8 15) (8 0 70 0.8 37) (8 0 63 0.84 24) (8 0 65 0.84 26) (8 0 70 0.84 17) (8 0 77 0.84 14) (8 0 81 0.84 14) (8 0 86 0.84 6) (8 0 70 0.88 25) (8 0 70 0.88 18) (8 0 77 0.92 26) (8 0 77 0.92 24) (8 0 81 0.92 29) (8 0 77 0.94 27) (0 9 40 0.64 18) (0 9 37 0.7 6) (0 9 44 0.72 19) (0 9 47 0.72 7) (0 9 47 0.72 16) (0 9 47 0.76 13) (0 9 68 0.78 35) (0 9 47 0.8 2) (0 9 54 0.84 35) (0 9 61 0.84 6) (0 9 71 0.84 15) (0 9 75 0.84 14) (0 9 89 0.84 18) (0 9 58 0.88 50) (0 9 59 0.88 25) (0 9 62 0.88 10) (0 9 79 0.88 33) (0 9 96 0.88 43) (0 9 58 0.92 35) (0 9 62 0.92 17) (0 9 70 0.92 27) (0 9 72 0.92 22) (0 9 75 0.92 16) (0 9 96 0.92 20) (0 9 75 0.94 37) (1 0 46 0.64 23) (1 0 42 0.68 4) (1 0 65 0.72 20) (1 0 46 0.76 42) (1 0 58 0.76 9) (1 0 42 0.8 32) (1 0 48 0.8 66) (1 0 58 0.8 28) (1 0 50 0.82 10) (1 0 80 0.82 4) (1 0 63 0.84 12) (1 0 65 0.84 17) (1 0 70 0.84 12) (1 0 70 0.84 23) (1 0 72 0.84 40) (1 0 97 0.84 18) (1 0 46 0.88 10) (1 0 56 0.88 38) (1 0 70 0.88 7) (1 0 70 0.88 23) (1 0 72 0.88 36) (1 0 76 0.88 9) (1 0 90 0.88 21) (1 0 76 0.92 62) (1 0 92 0.92 36) (1 1 21 0.68 23) (1 1 40 0.68 62) (1 1 44 0.72 28) (1 1 54 0.76 18) (1 1 36 0.78 10) (1 1 40 0.8 28) (1 1 56 0.8 22) (1 1 60 0.8 29) (1 1 48 0.84 15) (1 1 53 0.84 73) (1 1 60 0.84 10) (1 1 60 0.84 5) (1 1 65 0.84 13) (1 1 68 0.84 27) (1 1 60 0.88 20) (1 1 81 0.88 21) (1 1 81 0.88 12) (1 1 48 0.9 49) (1 1 48 0.9 17) (1 1 56 0.9 22) (1 1 68 0.9 71) (1 1 75 0.9 17) (1 1 81 0.9 10) (1 1 48 0.92 24) (1 1 68 0.92 18) (8 1 16 0.64 34) (8 1 19 0.64 6) (8 1 19 0.68 4) (8 1 32 0.72 22) (8 1 33 0.72 28) (8 1 33 0.74 31) (8 1 30 0.76 16) (8 1 42 0.76 27) (8 1 42 0.76 8) (8 1 33 0.78 32) (8 1 26 0.8 20) (8 1 30 0.8 35) (8 1 40 0.82 12) (8 1 54 0.82 14) (8 1 34 0.84 17) (8 1 34 0.84 29) (8 1 47 0.84 31) (8 1 47 0.84 6) (8 1 42 0.88 30) (8 1 47 0.88 27) (8 1 54 0.88 40) (8 1 54 0.88 19) (8 1 56 0.88 8) (8 1 60 0.88 8) (8 1 44 0.92 15) )))